It should be the best of times for American conservatism. Republican majorities in the House and Senate, a re-elected Republican president, an increasing number of Republican governors and a rightwards tilt in the judiciary. While the British Tories and German Christian Democrats flounder, America’s right seems to flourish. Well, that’s the cover story. Beneath the surface, however, American conservatism is in increasing trouble. The Republican coalition, always fragile, now depends as much on the haplessness of the Democrats as on its own internal logic. On foreign and domestic policy alike the American right is splintering. With no obvious successor to...