This is a foul electoral season, one conservative voters (or their children) will look back on with political regret and personal remorse. Mr. Trump’s “Mexican” slur about federal judge Gonzalo Curiel is the most shameful word uttered by a major presidential candidate since Dixiecrat Strom Thurmond thundered in 1948 against the “Nigra race.” As in 1948, Mr. Trump is appealing to constituents who have stuffed themselves on a diet of bad statistics and misleading anecdotes—people who fancy themselves victims but behave like bigots. Republican leaders who think they can co-opt or tame Mr. Trump will instead find themselves stained by him.

Meanwhile, let’s state clearly what shouldn’t need saying but does: Americans are blessed to have Mexico as our neighbor and Hispanics as our citizens. On this point, disagreement is indecency.