Speaker Nancy Pelosi’s announcement that the House will formally consider President Trump’s impeachment has plunged America into a constitutional crisis.

Mr. Trump smartly released the rough transcript of his July 25 conversation with Ukrainian President Volodymyr Zelensky. It undermines Mrs. Pelosi’s claim (made after the transcript’s release but before she had read it) that Mr. Trump “asked a foreign government to help him in his political campaign at the expense of our national security.” Yet don’t expect the president’s...