The impeachment process is barely underway and already some constitutional norms are being trampled without a note of media notice or political concern. To wit, can a whistleblower inside the intelligence bureaucracy override a President’s right to executive privilege merely with an accusation?

That seems to be the default view among Democrats and the press as they luxuriate in news about Donald Trump’s conversations with foreign leaders. First it was the call with Ukraine’s President. Then on Monday the leak was what Mr....