Opinion of the Court
Casey provided no clear answer to these questions. It said that a regulation is unconstitutional if it imposes a substantial obstacle "in a large fraction of cases in which [it] is relevant," 505 U. S., at 895, but there is obviously no clear line between a fraction that is "large" and one that is not. Nor is it clear what the Court meant by "cases in which" a regulation is "relevant." These ambiguities have caused confusion and disagreement. Compare Whole Woman's Health v. Hellerstedt, 579 U. S. 582, __ (2016) (slip op., at 39), with id., at __ (Alito, J., dissenting) (slip op., 24–25 & n. 11).
2
The difficulty of applying Casey's new rules surfaced in that very case. The controlling opinion found that Pennsylvania's 24-hour waiting period requirement and its informed-consent provision did not impose "undue burden[s]," Casey, 550 U. S., at 881–888 (plurality opinion), but Justice Stevens, applying the same test, reached the opposite result. Id., at 920–922 (Stevens, J., concurring in part and dissenting in part). That did not bode well, and then-Chief Justice Rehnquist aptly observed that "the undue burden standard presents nothing more workable than the trimester framework." Id., at 964–966 (Rehnquist, C. J., dissenting)
The ambiguity of the "undue burden" test also produced disagreement in later cases. In Whole Woman's Health v. Hellerstedt, the Court adopted the cost-benefit interpretation of the test, stating that that "[t]he rule announced in Casey … requires that courts consider the burdens a law imposes on abortion access together with the benefits those laws confer." 579 U. S. __, __ (2016) (slip op., at 19–20) (emphasis added). But five years later, a majority of the Justices rejected that interpretation. See June Medical, 591 U. S. __ (2020). Four Justices reaffirmed Whole Woman's Health's instruction to "weigh" a law's "benefits" against
