White House Counsel Pat Cipollone, who has faced repeated criticism over his legal strategy to fight impeachment, is again in the hot seat over his defense of President Donald Trump.

Cipollone will deliver opening arguments in the Senate impeachment trial this week. But the House impeachment managers, serving as prosecutors in the trial, claim the White House counsel's personal defense of Trump "threatens to undermine the integrity of the pending trial."

In a Tuesday letter to Cipollone, the managers said evidence gathered in the impeachment inquiry shows the top White House lawyer is a "material witness to the charges in both Articles of Impeachment for which President Trump now faces trial."

"Evidence indicates that, at a minimum, you have detailed knowledge of the facts regarding the first Articles and played an instrumental role in the conduct charged in the second Article," the letter reads.

The managers requested that "at a minimum, you must disclose all facts and information as to which you have first-hand knowledge that will be [an] 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."

It's a request that a judge might rule on during a typical trial. But, if Cipollone follows his pattern of refusing to comply with congressional requests for information as part of the impeachment proceedings, it seems unlikely that the top White House lawyer will go along with the ask. The White House did not provide a comment.

Cipollone's legal claims surrounding impeachment have been slammed by constitutional law scholars and other legal experts. His letters laying out the White House's refusal to participate in the impeachment inquiry have helped build the bulk of the article of impeachment for obstruction of Congress.

Another round of criticism landed over the holiday weekend when the White House filed its first legal brief in the trial, arguing that abuse of power and obstruction of Congress are not impeachable offenses.

They also claimed that a president must have violated "established law" in order to be impeached and removed from office.

"The Framers adopted a standard that requires a violation of established law to state an impeachable offense. By contrast, in their Articles of Impeachment, House Democrats have not even attempted to identify any law that was violated," the brief reads.

Also filed with that brief was a new Department of Justice Office of Legal Counsel opinion, finding that because the House did not take a full vote to authorize the impeachment inquiry before issuing subpoenas, those subpoenas are unlawful.

"A congressional committee's 'right to exact testimony and to call for the production of documents' is limited by the 'controlling charter' the committee has received from the House. Yet the House, by its rules, has authorized its committees to issue subpoenas only for matters within their legislative jurisdiction," the OLC memo, dated Jan. 19, reads. "Accordingly, no committee may undertake the momentous move from legislative oversight to impeachment without a delegation by the full House of such authority."

The White House trial memorandum filed Monday leans on that OLC opinion. Judges have questioned the weight given to the agency memos, and the Justice Department said in a December court filing that opinions from that office have "no force of law."

Cipollone doesn't have much trial experience. He did clerk for Judge Danny Brown on the U.S. Court of Appeals for the Sixth Circuit, and later worked on commercial litigation as a partner at Kirkland & Ellis and later for Stein, Mitchell Cipollone, Beato & Missner.

The White House counsel will be backed by a team of private lawyers, featuring former independent counsel Ken Starr, Harvard Law professor emeritus Alan Dershowitz and Robert Ray, who took over for Starr as independent counsel in the 1990s.

Dershowitz faced criticism over the weekend, as he claimed his past assertions during President Bill Clinton's impeachment that a crime did not have to be committed for an impeachable offense to have happened did not conflict with his current stance that the House had to find that Trump violated the law.

"I was saying that I am much more correct right now having done all the research, because that's the issue," Dershowitz told CNN's Anderson Cooper on Monday.

Questions have also been raised about Starr's claims during the Clinton impeachment that the use of executive privilege to block an investigation constitutes an impeachable offense.

A source close to Trump's legal team argued over the weekend that Clinton had wielded those powers differently than Trump, in blocking access to information about "private conduct."

"We will be very pleased with Judge Starr's presentation on how he's going to move this forward, what he sees are the issues, and the different aspects of the fact of the activities that we're involved in, in this situation with Bill Clinton's, are markedly different than what even the allegations are here," the source said.

But Starr's past words are now being used against Cipollone: The House managers, in their letter Tuesday, cited a 1984 opinion authored by Starr when he was sitting on the U.S. Court of Appeals for the D.C. Circuit, which upheld the dismissal of a lawsuit filed by an attorney after he was found to have created a potential conflict of interest.

"Moreover, part of the underlying rationale for the rule, namely that a lawyer's serving in a dual role of witness and advocate is unseemly, is directed at the protection of the public interest in continued respect for the legal profession rather than any waivable private interest," Starr wrote in the opinion.