Justice Stevens made a prescient prediction in footnote 13 of his dissent in McDonald v. City of Chicago, " [F]ederal courts will have little choice but to fix a highly flexible standard of review..."
They did not have to but they did whether it be Intermediate Scrutiny reduced to less than rational basis review or the insurmountable "substantial burden" hurdle.
"If federal and state courts must harmonize their review of gun-control laws under the Second Amendment, the resulting jurisprudence may prove significantly more deferential to those laws than the status quo ante. Once it has been established that a single legal standard must govern nationwide, federal courts will face a profound pressure to reconcile that standard with the diverse interests of the States and their long history of regulating in this sensitive area. Cf. Williams, 399 U.S., at 129-130, 90 S.Ct. 1914 (Harlan, J., concurring in result) (noting "`backlash'" potential of jot-for-jot incorporation); Grant, Felix Frankfurter: A Dissenting Opinion, 12 UCLA L.Rev. 1013, 1038 (1965) ("If the Court will not reduce the requirements of the fourteenth amendment below the federal gloss that now overlays the Bill of Rights, then it will have to reduce that gloss to the point where the states can live with it"). Amici argue persuasively that, post-"incorporation," federal courts will have little choice but to fix a highly flexible standard of review if they are to avoid leaving federalism and the separation of powers—not to mention gun policy—in shambles. See Brief for Brady Center to Prevent Gun Violence et al. as Amici Curiae (hereinafter Brady Center Brief)."