There’s an old saying that in politics there are no permanent victories—and no permanent defeats. Barry Goldwater was crushed in 1964 but the ideas that animated his candidacy found new life in the Reagan Revolution of 1980. Bill Clinton declared the era of big government over in 1996 and 14 years later we got ObamaCare.

The inevitable turning of the policy wheel should comfort conservatives unnerved by the prospect of a Hillary Clinton presidency. Liberals overreach. Statist solutions fail. Voters tire of one-party rule....