The story of Donald Trump’s phone call to Ukraine’s new president is unfolding in the familiar if depressing Trump-era pattern. An accusation leaks from an unidentified intelligence source about the President’s July 25 call, and his political and media opponents immediately conclude he has betrayed America and deserves censure or impeachment. Mr. Trump says the conversation was “perfectly fine and routine.” The public is left to sort the truth from the partisan histrionics.

Mr. Trump acknowledges that he asked Ukraine’s new...