Donald Trump leads the polls nationally and in most states in the race for the Republican presidential nomination. There are understandable reasons for his eminence, and he has shown impressive gut-level skill as a campaigner. But he is not deserving of conservative support in the caucuses and primaries. Trump is a philosophically unmoored political opportunist who would trash the broad conservative ideological consensus within the GOP in favor of a free-floating populism with strong-man overtones. Trump’s political opinions have wobbled all over the lot. The real-estate mogul and reality-TV star has supported abortion, gun control, single-payer health care à la...