Donald Trump’s economic program has gone through several revisions and now deserves a citation at Trump University for “most improved.” The candidate’s New York Economic Club speech on Thursday, which included new tax reform details, was an encouraging if sometimes contradictory performance.

Mr. Trump’s rhetoric is often grim, but in New York maybe for the first time he talked more about solutions than problems. He even mentioned unrealized human potential. “We reject the pessimism that says our standard of living can no longer...