For some inexplicable reason, conservatives rush towards fratricide with the same kind of urgency that drives lemmings over the cliff. It’s what they do, even when it’s counterproductive and costly. Conservatism wasn’t made better off by the four-year campaign waged against Speaker Newt Gingrich by some House conservatives who considered him ideologically unreliable. It wasn’t helped by John Boehner’s premature departure from Congress, brought about by political headaches caused by House Republicans on his right flank. A small group of so-called purists on the right even crossed swords with President Ronald Reagan, without whom modern conservatism would have emerged stillborn...