The sixth Republican debate on Thursday showed off a smaller top tier of candidates, who also showed that they’re getting better the more they debate. All of the contenders had their moments, but the main event was Donald Trump versus Ted Cruz, and Mr. Trump won handily with an big assist from “New York values,” of all things.

The Texas Senator this week said Mr. Trump “embodies New York values” as a way to suggest that the Manhattan businessman isn’t really a conservative. The two are fighting it out to finish first in the...