Compelling, overwhelming and bipartisan: These are the criteria Speaker Nancy Pelosi drew as she publicly announced last March that she wouldn’t support impeachment. Back then she claimed impeaching the president with anything less would be divisive and irresponsible. Ten months later, however, Mrs. Pelosi has transmitted two articles of impeachment that fail to meet any of her criteria, let alone those of the Founders.

As the Senate considers how to fulfill its constitutional role, Mrs. Pelosi’s words from March ring true....