It’s hard to imagine a greater victory for the conservative legal movement than the Supreme Court’s 2008 decision in District of Columbia v. Heller, which overturned D.C.’s ban on handguns. Not only did the Court definitively settle the long-contested question of whether the Second Amendment secures an individual right to keep and bear arms, but it did so using the language of “originalism”—the school of thought, long championed by conservatives, that says the Constitution should be read according to its original public meaning. It was therefore surprising when a leading conservative jurist, Judge J. Harvey Wilkinson III of the U.S....