Amid a Great Depression, and under tremendous pressure from a popular president and his huge congressional majority, however, this expert consensus gave way. The Supreme Court abandoned its laissez faire understanding of the Constitution’s Commerce Clause (among other provisions) so as to permit New Deal programs.

Rather, what it shows is that the United States periodically redefines the role of the federal government in society, in a process that is both political and legal — and, sometimes, more revolutionary than evolutionary. In that sense, we do have a “living Constitution.” …

Much has been made of the fact that Republicans had no objection, constitutional or otherwise, when the individual mandate first surfaced. But that was two decades ago. In today’s changed intellectual, fiscal and political environment, seemingly lapidary constitutional phrases such as “commerce . . . among the several states” can acquire fresh meaning, as they did for the New Deal and at other points in the past.