House Intelligence Committee Chairman Rep. Adam Schiff (D-CA) and the other House impeachment managers sent a letter Tuesday to White House Counsel Pat Cipollone seeking to disqualify him from representing President Donald Trump at the Senate trial.

The argument: because the articles of impeachment allege Trump committed “obstruction of Congress” by following legal advice to decline subpoenas, the lawyer who advised him is a “material fact witness.”

The letter argues: “Evidence indicates that, at a minimum, you have detailed knowledge of the facts regarding the first Article and played an instrumental role in the conduct charged in the second Article. The ethical rules generally preclude a lawyer from acting as an advocate at a trial in which he is likely also a necessary witness.”

If Cipollone is to represent the president, Schiff and the Democrats argue, he should have to “disclose all facts and information to which you have first-hand knowledge that will be at issue in connection with evidence you present or arguments you make in your role as the President’s legal advocate.”

In other words, Cipollone would have to violate attorney-client privilege and his duty of confidentiality to his client, effectively disqualifying him from participating.

The extraordinary letter is the latest in a series of bold — or desperate — tactics by House Democrats determined to retain control of an impeachment process that has passed into the hands of the Republican-controlled Senate.

Democrats are, in effect, arguing that the president does not have the right to any legal counsel other than counsel who follows their instructions — an echo of Schiff’s warning last year that any attempt to assert the president’s rights would be considered evidence of obstruction.

Ironically, Cippollone’s trial memorandum Monday responding to the House articles of impeachment argues that Schiff himself is an “interested fact witness” whose role made the entire House impeachment inquiry illegitimate.

The memorandum argued:

[T]he House’s factual investigation was supervised by an interested fact witness, Chairman Schiff, who—after falsely denying it—admitted that his staff had been in contact with the whistleblower and had given him guidance. See Part II.C. These three fundamental errors infected the underpinnings of this trial, and the Senate cannot constitutionally rely upon House Democrats’ tainted record to reach any verdict other than acquittal.

By Schiff’s own logic, he would have to be disqualified from prosecuting the case against the president, since he may be a witness.

The Senate trial begins Tuesday afternoon. Democrats have accused Senate Republicans of a “cover up” by adopting an accelerated schedule for what they once called an urgent process.

Joel B. Pollak is Senior Editor-at-Large at Breitbart News. He earned an A.B. in Social Studies and Environmental Science and Public Policy from Harvard College, and a J.D. from Harvard Law School. He is a winner of the 2018 Robert Novak Journalism Alumni Fellowship. He is also the co-author of How Trump Won: The Inside Story of a Revolution, which is available from Regnery. Follow him on Twitter at @joelpollak.