That's the provocative thesis advanced by David Bernstein in a new piece for Politico Magazine: If Trump wins the GOP nomination, he will be testing the limits of a strategy that has long haunted the Republican Party. Since the civil rights era, the Republicans have relied heavily upon white male voters in order to overcome a disadvantage among minorities and some subsets of women. Mathematically, that was an easier strategy a half-century ago, when white men dominated the electorate. But as the GOP failed to broaden its coalition and the demographics of America have shifted dramatically, an ever-greater percentage of...