666 ASHCROFT v. AMERICAN CIVIL LIBERTIES UNION Opinion of the Court In considering this question, a court assumes that certain protected speech may be regulated, and then asks what is the least restrictive alternative that can be used to achieve that goal. The purpose of the test is not to consider whether the challenged restriction has some effect in achieving Congress' goal, regardless of the restriction it imposes. The purpose of the test is to ensure that speech is restricted no further than necessary to achieve the goal, for it is important to ensure that legitimate speech is not chilled or punished. For that reason, the test does not begin with the status quo of existing regulations, then ask whether the challenged restriction has some additional ability to achieve Congress' legitimate interest. Any restriction on speech could be justified under that analysis. Instead, the court should ask whether the challenged regulation is the least restrictive means among available, effective alternatives. In deciding whether to grant a preliminary injunction, a district court must consider whether the plaintiffs have demonstrated that they are likely to prevail on the merits. See, e. g., Doran v. Salem Inn, Inc., 422 U. S. 922, 931 (1975). (The court also considers whether the plaintiff has shown irreparable injury, see ibid., but the parties in this case do not contest the correctness of the District Court's conclusion that a likelihood of irreparable injury had been established. See 31 F. Supp. 2d, at 497-498.) As the Government bears the burden of proof on the ultimate question of COPA's constitutionality, respondents must be deemed likely to prevail unless the Government has shown that respondents' proposed less restrictive alternatives are less effective than COPA. Applying that analysis, the District Court concluded that respondents were likely to prevail. Id., at 496497. That conclusion was not an abuse of discretion, because on this record there are a number of plausible, less restrictive alternatives to the statute. . The primary alternative considered by the District Court was blocking and filtering software. Blocking and filtering