Is the conversation that Republicans want to have about immigration any more serious than the one Democrats want to have about race?

The Republican presidential field sports no shortage of individuals capable of speaking intelligently about America’s broken immigration system. Sens. Marco Rubio and Lindsey Graham have drafted legislation on the issue. Jeb Bush co-wrote an entire book on the subject. And Rick Perry ran a border state with the nation’s second-largest immigrant population for 14 years. So why is Donald Trump,...