Trump nevertheless offers a valuable warning for the Republican party. If responsible men irresponsibly ignore an issue as important as immigration, it will be taken up by the reckless. If they cannot explain their Beltway maneuvers - worse, if their maneuvering is indefensible - they will be rejected by their own voters. If they cannot advance a compelling working-class agenda, the legitimate anxieties and discontents of blue-collar voters will be exploited by demagogues. We sympathize with many of the complaints of Trump supporters about the GOP, but that doesn't make the mogul any less flawed a vessel for them. Some...