JUSTICE O'CONNOR, with whom JUSTICE REHNQUIST joins, dissenting.
This Court's abortion decisions have already worked a major distortion in the Court's constitutional jurisprudence. See Akron v. Akron Center for Reproductive Health, Inc., 462 U. S. 416, 462 U. S. 452 (1983) (O'CONNOR, J., dissenting). Today's decision goes further, and makes it painfully clear that no legal rule or doctrine is safe from ad hoc nullification by this Court when an occasion for its application arises in a case involving state regulation of abortion. The permissible scope of abortion regulation is not the only constitutional issue on which this Court is divided, but -except when it comes to abortion -the Court has generally refused to let such disagreements, however longstanding or deeply felt, prevent it from evenhandedly applying uncontroversial legal doctrines to cases that come before it. See Heckler v. Chaney, 470 U. S. 821, 470 U. S. 838 (1985); id. at 470 U. S. 839 -840, n. 2 (BRENNAN, J., concurring) (differences over the validity of the death penalty under the Eighth Amendment should not influence the Court's consideration of a question of statutory administrative law). That the Court's unworkable scheme for constitutionalizing the regulation of abortion has had this institutionally debilitating effect should not be surprising, however, since the Court is not suited to the expansive role it has claimed for itself in the series of cases that began with Roe v. Wade, 410 U. S. 113 (1973).
The Court today holds that "[t]he Court of Appeals correctly invalidated the specified provisions of Pennsylvania's 1982 Abortion Control Act." Ante at 476 U. S. 772. In so doing, the Court prematurely decides serious constitutional questions on an inadequate record, in contravention of settled principles of constitutional adjudication and procedural fairness. The constitutionality of the challenged provisions was not properly before the Court of Appeals, and is not properly before this Court. There has been no trial on the merits, and appellants have had no opportunity to develop facts that might have a bearing on the constitutionality of the statute. The only question properly before the Court is whether or not a preliminary injunction should have been issued to restrain enforcement of the challenged provisions pending trial on the merits. This Court's decisions in Akron v. Akron Center for Reproductive Health, supra, Planned Parenthood Assn. of Kansas City, Missouri, Inc. v. Ashcroft, 462 U. S. 476 (1983), and Simopoulos v. Virginia, 462 U. S. 506 (1983), do not establish a likelihood that appellees would succeed on the merits of their constitutional claims sufficient to warrant overturning the District Court's denial of a preliminary injunction. Under the approach to abortion regulation outlined in my dissenting opinion in Akron, to which I adhere, it is even clearer that no preliminary injunction should have issued. I therefore dissent.
I
The only issue before the District Court in this case was whether to grant appellees' motion for a preliminary injunction against enforcement of Pennsylvania's Abortion Control Act. The limited record before the District Court consisted of affidavits submitted by appellees, the parties' memoranda of law, the Act itself, including the findings of the Pennsylvania Legislature, and a stipulation of uncontested facts. As the District Judge noted, this stipulation "was entered into solely for the purpose of the motion for preliminary injunction." 552 F.Supp. 791, 794, n. 1 (ED Pa.1982). Indeed, the parties expressly provided that the stipulation should be "without prejudice to any party's right to controvert any facts or to prove any additional facts at any later proceeding in this action." App. 9a-10a. In light of the stipulation of uncontested facts, no testimony or evidence was submitted at the hearing on the motion for a preliminary injunction.
In these circumstances, the District Judge's consideration of the motion before him was governed by the black letter law recapitulated in University of Texas v. Camenisch, 451 U. S. 390, 451 U. S. 395 (1981):
The purpose of a preliminary injunction is merely to preserve the relative positions of the parties until a trial on the merits can be held. Given this limited purpose, and given the haste that is often necessary if those positions are to be preserved, a preliminary injunction is customarily granted on the basis of procedures that are less formal, and evidence that is less complete, than in a trial on the merits. A party thus is not required to prove his case in full at a preliminary injunction hearing, and the findings of fact and conclusions of law made by a court granting a preliminary injunction are not binding at trial on the merits. In light of these considerations, it is generally inappropriate for a federal court, at the preliminary injunction stage, to give a final judgment on the merits. Should an expedited decision on the merits be appropriate, Rule 65(a)(2) of the Federal Rules of Civil Procedure provides a means of securing one. That Rule permits a court to 'order the trial of the action on the merits to be advanced and consolidated with the hearing of the application.' Before such an order may issue, however, the courts have commonly required that the parties should normally receive clear and unambiguous notice of the court's intent to consolidate the trial and the hearing] either before the hearing commences or at a time which will still afford the parties a full opportunity to present their respective cases.
(Citations omitted.)
The District Judge scrupulously adhered to these settled principles. He granted the preliminary injunction as to one provision of the Act, and denied preliminary relief as to all the other challenged provisions. Having seen no occasion to issue a Rule 65 order, he properly refrained from rendering final judgment on the merits by declaratory judgment or otherwise. That the District Judge understood the preliminary nature of the proceedings, and ruled accordingly, is incontrovertible:
I have applied the traditional criteria applicable to a motion for preliminary injunction: likelihood of success on the merits, irreparable harm if the relief is not granted, possibility of harm to the nonmoving party, and, where relevant, harm to the public. Given the importance of the right involved in this litigation, I have assumed that, if the plaintiffs were able to show likelihood of success on the merits, then the irreparable harm requirement would be met. I conclude that, in only one instance, the 24-hour waiting period, did the plaintiffs carry their burden of demonstrating likelihood of success on the merits. * * * *" My adjudication is limited to the plaintiffs' request for apreliminary injunction. It is circumscribed by the record produced by the parties and the arguments advanced in the briefs on this motion. After applying the criteria for a preliminary injunction, I conclude that the only portion of the Act which the plaintiffs have demonstrated should be preliminarily enjoined is the 24-hour waiting period. In all other respects, the plaintiffs have failed to show a right to a preliminary injunction pending the outcome of the trial on the merits.
552 F.Supp. at 811 (emphasis in original).
The District Judge correctly discerned that
[t]he traditional standard for granting a preliminary injunction requires a plaintiff to show that, in the absence of its issuance, he will suffer irreparable injury, and also that he is likely to prevail on the merits.
Doran v. Salem Inn, Inc., 422 U. S. 922, 422 U. S. 931 (1975). Unsurprisingly, the likelihood of success on the merits emerged, in the District Judge's view, as the most important factor in determining whether an injunction should issue in this case. In sum, when the District Judge denied appellees' motion for a preliminary injunction, he faithfully applied uncontroversial criteria for ruling on such motions and rendered a decision that "was not in any sense intended as a final decision as to the constitutionality of the challenged statute." Brown v. Chote, 411 U. S. 452, 456 (1973).
When the appeal was taken to the Court of Appeals for the Third Circuit, that court's review should have been limited to determining whether the District Court had abused its discretion in denying preliminary relief. Doran, supra, at 422 U. S. 931 -932; Brown, supra, at 411 U. S. 457. If the Court of Appeals concluded that the District Court had committed legal errors that infected its assessment of the likelihood that appellees would succeed on the merits, the Court of Appeals should then have addressed the remaining factors that make up the preliminary injunction inquiry. If it concluded that denial of the preliminary injunction was an abuse of discretion, it should have entered judgment providing for entry of a preliminary injunction. What it should not have done, and what it did do, was to issue a final, binding declaration on the merits of appellees' constitutional claims.
The Court concedes that a court of appeals should ordinarily review the denial of a preliminary injunction under an abuse of discretion standard, and it concedes that a court of appeals should ordinarily confine itself to assessing the "probability that the plaintiffs would succeed on the merits." Ante at 476 U. S. 755. But the Court purports to find an exception to this rule in the decisions in Youngstown Sheet & Tube Co. v. Sawyer, 343 U. S. 579 (1952), and Smith v. Vulcan Iron Works, 165 U. S. 518 (1897). It asserts that these cases indicate that,
if a district court's ruling rests solely on a premise as to the applicable rule of law, and the facts are established or of no controlling relevance, that ruling may be reviewed even though the appeal is from the entry of a preliminary injunction.
Ante at 476 U. S. 757. The Court then announces that the requirement that appellate review proceed under the deferential abuse of discretion standard is "a rule of orderly judicial administration, not a limit on judicial power." Ibid. Postulating that the Court of Appeals had a "full record before it on the issues now before us," ibid., the Court concludes that this "full record," and the fact that this Court's decisions in Akron, Ashcroft, and Simopoulos were handed down during the pendency of the appeal, justified the Court of Appeals "in proceeding to plenary review of those issues." Ante at 476 U. S. 757.
This analysis mischaracterizes the proceedings in the District Court and is unsupported by precedent or logic. No one doubts that the legal premises on which the District Judge proceeded were reviewable. But the fact is that the District Judge did not make the final, definitive "ruling" on the merits the Court imputes to him. The only "ruling" the Court of Appeals had before it with respect to the merits was a determination of "likelihood of success" based on facts which were stipulated only for purposes of the preliminary injunction motion, and on arguments framed with a view toward only those facts. Nor was there a "full record" upon which the Court of Appeals could decide the merits. The Court falls into precisely the error pointed out in Camenisch, 451 U.S. at 451 U. S. 394, where this Court unanimously rejected the proposition that determinations on the propriety of preliminary relief are "tantamount to decisions on the underlying merits," because that view
improperly equates 'likelihood of success' with 'success,' and, what is more important,… ignores the significant procedural differences between preliminary and permanent injunctions.
The Court of Appeals was convinced that the District Judge, in reliance on the decisions of the Courts of Appeals that were later reviewed in Akron and Ashcroft, had taken a view of the applicable law which this Court's decisions in those cases demonstrated to be erroneous. Citing Apple Computer, Inc. v. Franklin Computer Corp., 714 F.2d 1240, 1242 (CA3 1983), cert. dism'd under this Court's Rule 53, 464 U.S. 1033 (1984), the Court of Appeals stated that
[t]he customary discretion accorded to a district court's ruling on a preliminary injunction yields to our plenary scope of review as to the applicable law.
737 F.2d 283, 290 (1984). Apple Computer, in turn, relied on Judge Friendly's opinion for the Second Circuit in Donovan v. Bierwirth, 680 F.2d 263, 269, cert. denied, 459 U.S. 1069 (1982):
Despite oft-repeated statements that the issuance of a preliminary injunction rests in the discretion of the trial judge, whose decisions will be reversed only for 'abuse,' a court of appeals must reverse if the district court has proceeded on the basis of an erroneous view of the applicable law, or of the standards governing the granting or denial of interlocutory relief.
(Citations omitted.)
Donovan's reasoning, however, goes only to the standard of appellate review, not to the extent of the issues to be reviewed. Whether or not Donovan's approach is sound, it is clear that a district court does not have discretion to rule on the basis of a misapprehension of controlling law. But even assuming, arguendo, that, where a court of appeals detects such an error, it may then engage in de novo review of the determination whether a preliminary injunction should issue, see 680 F.2d at 270, such discretion does not ordinarily extend to deciding the merits of the controversy with finality. Judge Friendly did no such thing in Donovan, id. at 276, nor did the Third Circuit in Apple Computer, see 714 F.2d at 1242.
What is at issue here is a matter of legal principle. As JUSTICE BLACKMUN has observed on a previous occasion:
The distinction between the preliminary and final injunction stages of a proceeding is more than mere formalism. The time pressures involved in a request for a preliminary injunction require courts to make determinations without the aid of full briefing or factual development, and make all such determinations necessarily provisional.
Firefighters v. Stotts, 467 U. S. 561, 467 U. S. 603 -604, n. 7 (1984) (dissenting opinion). The holding of the Court today thus comes at the expense of the basic principle underlying the framework set out in Camenisch for ruling on a motion for a preliminary injunction: that fairness to the parties and reliable adjudication of disputes require final, binding rulings on the merits of a controversy to be made only after each side has had an opportunity to establish its version of the disputed facts, or to establish that the facts are not in dispute.
Equally neglected by the Court is a second principle, closely related to the first:
Ordinarily, an appellate court does not give consideration to issues not raised below. For our procedural scheme contemplates that parties shall come to issue in the trial forum vested with authority to determine questions of fact. This is essential in order that parties may have the opportunity to offer all the evidence they believe relevant to the issues which the trial tribunal is alone competent to decide; it is equally essential in order that litigants may not be surprised on appeal by final decision there of issues upon which they have had no opportunity to introduce evidence.
Hormel v. Helvering, 312 U. S. 552, 312 U. S. 556 (1941). See also Singleton v. Wulff, 428 U. S. 106, 428 U. S. 120 -121 (1976); cf. Fountain v. Filson, 336 U. S. 681, 336 U. S. 683 (1949) (per curiam) (reversing a summary judgment order "made on appeal on a new issue as to which the opposite party had no opportunity to present a defense before the trial court"). The cases on which the Court relies simply do not support the short shrift the Court gives these basic principles.
In Youngstown Sheet & Tube Co., President Truman, invoking an immediate threat to the national defense precipitated by a threatened nationwide strike in the steel industry, ordered the Secretary of Commerce to seize the steel mills and keep them running. 343 U.S. at 343 U. S. 583. The steel companies sought a declaratory judgment, a preliminary injunction, and a permanent injunction against the seizure, on the grounds that the President had no authority to order it. Ibid. Although the District Court had before it only "motions for temporary injunctions" when it ruled, 103 F.Supp. 569, 572 (DC 1952), "in the light of the facts presented, the District Court saw no reason for delaying decision of the constitutional validity of the orders." Youngstown Sheet & Tube Co., supra, at 343 U. S. 585. Indeed, the District Court had
com[e] to a fixed conclusion… that defendant's acts are illegal…. Nothing that could be submitted at such trial on the facts would alter the legal conclusion I have reached.
103 F.Supp. at 576.
Thus, the District Court's preliminary injunction in Youngstown Sheet & Tube Co. rested on what amounted to a declaratory judgment that the orders were constitutionally invalid. That in itself was a pronounced departure from normal practice, although one that this Court found proper in the highly unusual circumstances presented in Youngstown Sheet & Tube Co., where time was manifestly of the essence, * and there was no contention that the Government had been deprived of an opportunity to present facts that could have altered the resolution of the constitutional question. To the contrary, when
[p]laintiffs moved for a preliminary injunction before answer or hearing, [d]efendant opposed the motion, filing uncontroverted affidavits of Government officials describing the facts underlying the President's order.
343 U.S. at 343 U. S. 678 (Vinson, C.J., dissenting).
Neither of the foregoing justifications for the District Court's unusual decision to reach the merits in Youngstown Sheet & Tube is present here. No emergency remotely comparable to the one in Youngstown Sheet & Tube confronted the Court of Appeals, which granted appellees' motion to enjoin enforcement of the entire Act pending appeal, and withheld judgment until after this Court had ruled in Akron and its companion cases. 737 F.2d at 290. Appellants conceded in the Court of Appeals that several provisions of the Abortion Act were unconstitutional in the wake of those decisions, but appellants did not concede that the provisions on which the Court of Appeals dispositively ruled were unconstitutional. Nor is there any suggestion that appellants conceded in the Court of Appeals that there were no factual issues that could have a bearing on the constitutionality of these provisions. Consequently, even if a preliminary injunction should have issued, the proper course would have been to remand for final determination of the merits.
Indeed, since Youngstown Sheet & Tube Co. was decided, this Court has expressly reaffirmed that
a state statute should not be declared unconstitutional by a district court if a preliminary injunction is granted a plaintiff to protect his interests during the ensuing litigation.
Withrow v. Larkin, 421 U. S. 35, 421 U. S. 43 (1975). See Mayo v. Lakeland Highlands Canning Co., 309 U. S. 310 (1940). If it is improper for a district court to enter such a declaratory judgment when it grants a preliminary injunction, then a fortiori it is improper for a court of appeals to do so when the district court has only appraised the likelihood of success on the merits. What happened here is even more extreme: the Court of Appeals, reviewing the denial of a preliminary injunction, held in the first instance that nothing that could be submitted at a trial on the merits would alter its conclusion that "most of the provisions attacked by appellants are unconstitutional as a matter of law." 737 F.2d at 287. Nothing in Youngstown Sheet & Tube Co. remotely suggests that it was proper for the Court of Appeals to take this extraordinary step.
Camenisch makes clear that a determination of a party's entitlement to a preliminary injunction is a separate issue from the determination of the merits of the party's underlying legal claim, and that a reviewing court should not confuse the two.
Stotts, 467 U.S. at 467 U. S. 603 (BLACKMUN, J., dissenting).
The Court strays even further afield when it invokes Smith v. Vulcan Iron Works in defense of the Court of Appeals' decision to reach and resolve the merits despite the fact that the District Court had not done so and without giving the parties "the benefit… of a full opportunity to present their cases." Camenisch, 451 U.S. at 451 U. S. 396. The trial court in Smith,
upon a bill in equity for the infringement of a patent for an invention… entered an interlocutory decree, adjudging that the patent was valid and had been infringed, granting an injunction, and referring the case to a master to take an account of profits and damages.
165 U.S. at 165 U. S. 518 (emphasis added). The defendant challenged the trial court's alleged "error in holding that the patent was valid, and that it had been infringed." Ibid. The Circuit Court of Appeals reversed the decree, rejecting the plaintiff's contention that it could rule only on "whether an injunction should be awarded." Ibid. This Court held that, under the plain language of the statute conferring jurisdiction on the Circuit Court of Appeals, an appeal was authorized "from the whole of such interlocutory order or decree, and not from that part of it only which grants or continues an injunction," and consequently the statute conferred "authority to consider and decide the case upon its merits." Id. at 165 U. S. 525. The trial court, of course, had already done precisely that, deciding the issue of liability after the parties had joined issue on the merits, while referring the matter of damages to a master. Reliance on Smith in this case is therefore misplaced, for, to repeat, the District Court did not decide -and could not properly have decided -the merits of appellees' constitutional claims when it refused to grant a preliminary injunction.
The Court also seeks comfort in an analogy to the rule that a federal court need not abstain, pending state court review, from reviewing a constitutional challenge to the validity of a state statute that is not fairly subject to an interpretation that will avoid the constitutional question. Zwickler v. Koota, 389 U. S. 241, 389 U. S. 251, and n. 14 (1967). When a federal district court declines to abstain, however, it does not, in so doing, decide the merits of the constitutional question even if the parties have not had a full opportunity to air them. The court simply proceeds to decide the case in accordance with the normal procedural requirements that safeguard the parties' rights to be heard. A refusal to abstain therefore infringes neither the principle that final judgment should follow a full opportunity to be heard on the factual and legal merits of the case nor the principle that "parties shall come to issue in the trial forum vested with authority to determine questions of fact." Hormel, 312 U.S. at 312 U. S. 556. The same cannot be said of what the Court of Appeals did here.
Whatever the exceptions which would justify a district court in finally resolving an issue on the merits at the preliminary injunction stage, no such exception was applicable here. Nor is this a case in which the court of appeals was justified in resolving an issue not passed on in the district court because proper resolution was beyond any doubt or grave injustice might result from failure to do so. See Singleton v. Wulff, 428 U.S. at 428 U. S. 121. The Court of Appeals not only decided to stand in the shoes of the District Court by ruling on an issue not passed upon below -it ruled on an issue on which, absent extraordinary circumstances, the District Court could not have ruled without " clear and unambiguous notice'" that would "`afford the parties a full opportunity to present their respective cases.'" Camenisch, supra, at 451 U. S. 395. The Court attempts to veil the impropriety of its decision to affirm on the merits despite the procedural posture of this case by implying that the challenged provisions are patently unconstitutional. But this claim too is unsupported in this Court's decisions concerning state regulation of abortion.
The discretionary exception the Court fashions today will also prove vexatious to administer. Parties now face the risk that a final ruling on the merits will be entered against them by a court of appeals when an appeal is taken from the grant or denial of a motion for a preliminary injunction, although the district court made only an initial assessment of the likelihood that the moving party would succeed on the merits. It is predictable that parties will respond by attempting to turn preliminary injunction proceedings into contests over summary judgment or full-scale trials on the merits. That tendency will make the preliminary injunction less useful in serving its intended function of preserving the status quo pending final judgment on the merits, while making litigation more expensive, less reliable, and less fair. If this case did not involve state regulation of abortion, it may be doubted that the Court would entertain, let alone adopt, such a departure from its precedents.
II
In this Court, appellants argue that the judgment of the Court of Appeals should be vacated and the District Court's denial of a preliminary injunction sustained. Appellants have stated that they "intend to present to the District Court a complete factual record which… could affect the disposition of this case," and have indicated some of the specific factual propositions they would seek to establish. Brief for Appellants 44-48. At oral argument, counsel for appellants reiterated that, with the exception of the second physician requirement, "there are additional justifications by way of facts that we can offer" as to each of the challenged provisions. Tr. of Oral Arg. 13. These assertions alone would justify vacating the judgment of the Court of Appeals insofar as that court did more than direct the entry of a preliminary injunction. In Singleton v. Wulff, supra, at 428 U. S. 120, for example, this Court reversed the Court of Appeals' decision to reach the merits of that case, even though this Court had "no idea what evidence, if any, petitioner would, or could, offer in defense of this statute," because it was clear that "petitioner has had no opportunity to proffer such evidence." I would apply that reasoning here even if I were not persuaded that, as to several of the challenged provisions, additional factual development -for example, facts concerning the costs associated with the reporting and informed consent provisions, and the extent of the problems Pennsylvania was seeking to correct -could affect the decision on the merits. Appellants should not have to prove that they are entitled to an opportunity to be heard.
Since it rendered "what amounts to a final declaratory judgment on the constitutionality of the statute," ante at 476 U. S. 806 (WHITE, J., dissenting), the Court of Appeals necessarily believed that, in light of Akron and its companion cases, appellees had established a sufficient likelihood of success on the merits to warrant issuance of a preliminary injunction. Pennsylvania contends that this ruling is erroneous even under the supervening decisions of this Court. In the alternative, Pennsylvania suggests that the facial constitutionality of the challenged provisions of its Abortion Act may be sustained on this record.
I agree with much of what JUSTICE WHITE has written in 476 U. S. and the arguments he has framed might well suffice to show that the provisions at issue are facially constitutional. Nonetheless, I believe the proper course is to decide this case as the Court of Appeals should have decided it, lest appellees suffer the very prejudice the Court sees fit to inflict on appellants. For me, then, the question is not one of "success," but of the "likelihood of success." In addition, because Pennsylvania has not asked the Court to reconsider or overrule Roe v. Wade, 410 U. S. 113 (1973), I do not address that question.
I do, however, remain of the views expressed in my dissent in Akron, 462 U.S. at 462 U. S. 459 -466. The State has compelling interests in ensuring maternal health and in protecting potential human life, and these interests exist "throughout pregnancy." Id. at 462 U. S. 461 (O'CONNOR, J., dissenting). Under this Court's fundamental-rights jurisprudence, judicial scrutiny of state regulation of abortion should be limited to whether the state law bears a rational relationship to legitimate purposes such as the advancement of these compelling interests, with heightened scrutiny reserved for instances in which the State has imposed an "undue burden" on the abortion decision. Id. at 462 U. S. 461 -463 (O'CONNOR, J., dissenting). An undue burden will generally be found "in situations involving absolute obstacles or severe limitations on the abortion decision," not wherever a state regulation "may inhibit' abortions to some degree." Id. at 462 U. S. 464 (O'CONNOR, J., dissenting). And if a state law does interfere with the abortion decision to an extent that is unduly burdensome, so that it becomes "necessary to apply an exacting standard of review," id. at 462 U. S. 467 (O'CONNOR, J., dissenting), the possibility remains that the statute will withstand the stricter scrutiny. See id. at 462 U. S. 473 -474 (O'CONNOR, J., dissenting); Ashcroft, 462 U.S. at 462 U. S. 505 (O'CONNOR, J., concurring in judgment in part and dissenting in part).
These principles for evaluating state regulation of abortion were not newly minted in my dissenting opinion in Akron. Apart from Roe's outmoded trimester framework, the "unduly burdensome" standard had been articulated and applied with fair consistency by this Court in cases such as Harris v. McRae, 448 U. S. 297, 448 U. S. 314 (1980), Maher v. Roe, 432 U. S. 464, 432 U. S. 473 (1977), Beal v. Doe, 432 U. S. 438, 432 U. S. 446 (1977), and Bellotti v. Baird, 428 U. S. 132, 428 U. S. 147 (1976). In Akron and Ashcroft, the Court, in my view, distorted and misapplied this standard, see Akron, 462 U.S. at 462 U. S. 452 -453 (O'CONNOR, J., dissenting), but made no clean break with precedent, and indeed "follow[ed] this approach" in assessing some of the regulations before it in those cases. Id. at 462 U. S. 463 (O'CONNOR, J., dissenting).
The Court today goes well beyond mere distortion of the "unduly burdensome" standard. By holding that each of the challenged provisions is facially unconstitutional as a matter of law, and that no conceivable facts appellants might offer could alter this result, the Court appears to adopt as its new test a per se rule under which any regulation touching on abortion must be invalidated if it poses "an unacceptable danger of deterring the exercise of that right." Ante at 476 U. S. 7