Vice President Biden recently called for the impeachment of President Trump, explaining, "He is shooting holes in our Constitution. We cannot let him get away with it." Mr. Biden's concern for the Constitution is touching. So long as he is on the topic of our nation's basic law, though, let him also direct his attention to Massachusetts' senior senator, Elizabeth Warren, who is emerging as his most formidable rival for the Democratic presidential nomination. Mrs. Warren's presidential ca...