The United States Senate has voted, along virtually strict party lines, not to call witnesses on the two key charges in the impeachment trial of the President: that President Trump abused his power by withholding military aid to Ukraine, and that he also obstructed Congress by refusing to participate in the House’s impeachment investigation. Given this outcome, the acquittal of the President is virtually assured to come Wednesday.

The Senate’s decision rests on this narrow but controversial definitional question: What is an impeachable offense? This past December, a “Letter to Congress” signed by over 800 constitutional law professors defended the legal position that “conduct need not be criminal to be impeachable. The standard here is constitutional; it does not depend on what Congress has chosen to criminalize. Impeach is a remedy for grave abuses of the public trust.”

More recently, a similar legal position was taken by one of Trump’s more eloquent defenders, Professor Jonathan Turley of the George Washington University Law School. He attacked Harvard’s Emeritus Professor Alan Dershowitz for claiming impeachment of the President requires the commission of some criminal act, something that was not alleged in the House’s impeachment articles. But unlike the Professors’ Letter to Congress, Turley sought to split the difference: “I do not believe that the House managers have sufficiently rebutted the defense of the president and specifically established the necessary intent to hold the Ukrainian aid for solely political purposes (as opposed to a policy concern of corruption or sharing costs with allies).” But, he continued, “I still believe that [Dershowitz] is fundamentally wrong in maintaining that impeachable offenses must be based on actual crimes or ‘crime-like’ conduct.”