House Democrats are charging that a lawyer on President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE's defense team is a "fact witness," arguing that he must disclose all his first-hand involvement to the Senate and Supreme Court Chief Justice John Roberts in order to prevent any conflicts of interest ahead of the Senate impeachment trial.

The team of House impeachment managers in a Tuesday letter to White House counsel Pat Cipollone claimed that Cipollone's office was directly involved in key events that are at the center of their impeachment case, raising concerns about his role defending the president from charges of abuse of power and obstruction of justice.

“In preparation for the trial of Donald J. Trump before the Senate, we write to notify you that evidence received by the House of Representatives during its impeachment inquiry indicates that you are a material witness to the charges in both Articles of Impeachment for which President Trump now faces trial," the impeachment managers team wrote.

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“You must disclose all facts and information as 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 so that the Senate and Chief Justice can be apprised of any potential ethical issues, conflicts, or biases," they continue.

They allege that Cipollone was part of the administration's "efforts to conceal" Trump's decision to withhold aid to Ukraine as leverage to pressure the foreign power to investigate a 2020 political foe, that he briefed Trump on the whistleblower allegations and that he was also part of the president's legal team that sought to block former and current administration officials from testifying as part of the House impeachment inquiry.

"In light of your extensive knowledge of these key events, your personal representation of President Trump threatens to undermine the integrity of the pending trial. You may be a material witness to the charges against President Trump even though you are also his advocate," they write.

The White House ripped the Democratic argument, calling it an absurd political stunt.

“The Democrats are an utter joke - they have no case, and this latest political stunt proves it," White House principal deputy press secretary Hogan Gidley said in a statement. "The idea that the Counsel to the President has to turn over protected documents and confidential information is ludicrous, and to imply he can’t represent the President of the United States in an impeachment proceeding is completely absurd.”

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“Further, the man Democrats appointed to lead these proceedings is Adam Schiff - who has been caught lying multiple times about Russia collusion evidence that didn’t exist, made up a totally phony phone conversation about Ukraine that never happened, and lied that his staff didn’t have contact with the whistleblower. If there’s anyone who should be disqualified from leading this proceeding it’s Mr. Schiff," Gidley said.

The anonymous whistleblower whose allegations triggered the House impeachment inquiry contacted the House Intelligence Committee before going through the whistleblower process. An aide for the committee spoke to Schiff, but did not provide the individual's name.

Democrats, in response to these calls, have shot back that Republicans are seeking to misdirect the focus: This impeachment inquiry is into the conduct of the president and his associates.

The letter comes one day before House Democrats are poised to begin their arguments before the GOP-controlled Senate as to why Trump should be impeached and removed from office.

Democrats allege that Trump withheld nearly $400 million in U.S. aid to Ukraine and the promise of a White House meeting to pressure Ukrainian President Volodymyr Zelensky to open two politically motivated investigations, including a corruption probe into former Vice President Joe Biden Joe BidenSenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE, who is running for president, and his son Hunter Biden.

They allege that Trump then sought to cover up his actions by obstructing the congressional investigation into his contacts with Kyiv, asserting absolute immunity and blocking the testimony of former and current White House officials from differing levels of seniority in the administration from testifying in the impeachment inquiry.

House Democrats impeached Trump last month largely along party lines on two articles of impeachment: abuse of power and obstruction of justice.

The highly partisan process has since moved to the upper chamber, where both sides will seek to win the PR battle in a high-stakes election year.