If you ask Republicans what their party stands for, most will say conservatism. The trouble comes in trying to define what that means.

Which should come first—nationalism or resisting the growth of the state? Is the existing social order sound, or is our moral decay so serious that more radical solutions are needed? Is the wealth accumulating in our big coastal cities a sign of entrepreneurial vitality or of corruption and cronyism? Donald Trump’s rise has put these cleavages into sharp relief, but they have been shaping...