WASHINGTON -- U.S. President Donald Trump is adding experience in constitutional law and the politics of impeachment to his legal defence team, bringing in retired law professor Alan Dershowitz and Ken Starr, the independent counsel who investigated President Bill Clinton.

In adding the two men, Trump is turning to a pair of brand-name attorneys who have experience in some of the more consequential legal dramas of recent American history and whose presence is likely to add to the made-for-television feel of the impeachment trial. Both are regular guests on Fox News, the president's preferred television network, and have put forth defences of the president during their appearances.

Dershowitz, a former Harvard professor, is a constitutional expert who in recent years has supported Trump's expansive view of presidential powers, while Starr is a veteran of the last partisan impeachment fight. His investigation into Clinton's relationship with former White House intern Monica Lewinsky led to Clinton's impeachment over 20 years ago. Clinton was acquitted by the Senate.

The lead roles for Trump's defence will be played by White House Counsel Pat Cipollone and Trump personal lawyer Jay Sekulow.

The team will also include Pam Bondi, the former Florida attorney general and a Trump ally, according to a person who spoke to The Associated Press on condition of anonymity because the person wasn't authorized to speak on the record.

Dershowitz confirmed his role in a series of tweets on Friday, saying, he would "present oral arguments at the Senate trial to address the constitutional arguments against impeachment and removal."

Dershowitz said of himself: "While Professor Dershowitz is nonpartisan when it comes to the Constitution -- he opposed the impeachment of President Bill Clinton and voted for Hillary Clinton -- he believes the issues at stake go to the heart of our enduring Constitution."

A Fox News host said on the air that Starr would be parting ways with the network as a result of his role on the legal team.

Other members of Trump's legal defence include Jane Raskin, who was part of the president's legal team during special counsel Robert Mueller's Russia investigation, and Robert Ray, who was part of the the Whitewater investigation of the Clintons.

The White House would not confirm the roster of the president's attorneys, and some officials bristled that the announcement was not co-ordinated with them. White House attorneys and the outside legal team were still discussing how political the formal legal brief should be.

The president faces a noon Monday deadline to file his brief in the trial, and the legal team was still being drafted, according to a person familiar with the situation.

Trump was impeached on charges of abuse of power and obstructing Congress ,stemming from his pressure on Ukraine to investigate Democratic rivals as he was withholding security aid, and obstructing the ensuing congressional probe.

The U.S. Senate opened the trial on Thursday and senators were sworn in as jurors. The trial resumes Tuesday.

The president insists he did nothing wrong, and he complains about his treatment daily, sometimes distracting from unrelated events. On Friday, as Trump invited the championship LSU football team to the Oval Office for photos, he said the space had seen "a lot of presidents, some good, some not so good. But you got a good one now, even though they're trying to impeach the son of a bitch. Can you believe that?"

While he speaks dismissively of the case, new revelations are mounting about Trump's actions toward Ukraine.

The Government Accountability Office said Thursday that the White House violated federal law in withholding the security assistance to Ukraine, which shares a border with hostile Russia.

At the same time, an indicted associate of Trump's personal lawyer Rudy Giuliani, Lev Parnas, has turned over to prosecutors new documents linking the president to the shadow foreign policy being run by Giuliani.

Those developments applied fresh pressure to senators to call more witnesses for the trial, a main source of contention that is still to be resolved. The White House has instructed officials not to comply with subpoenas from Congress requesting witnesses or other information.

Besides his 1990s role as an independent counsel, Starr is also a former U.S. solicitor general and federal circuit court judge.

He was removed as president of Baylor University and then resigned as chancellor of the school in the wake of a review critical of the university's handling of sexual assault allegations against football players. Starr said his resignation was the result of the university's board of regents seeking to place the school under new leadership following the scandal, not because he was accused of hiding or failing to act on information.

Dershowitz's reputation has been damaged in recent years by his association with Jeffrey Epstein, the millionaire who killed himself in jail last summer while awaiting trial on charges that he sexually abused multiple underage girls.

One of Epstein's alleged victims, Virginia Roberts Giuffre, has accused Dershowitz of participating in her abuse. Dershowitz has denied it and has been battling in court for years with Giuffre and her lawyers. He recently wrote a book rejecting her allegations, called "Guilt by Accusation." Giuffre and Dershowtiz are also suing each other for defamation, each saying the other is lying.

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Associated Press writer Zeke Miller in Washington and David Caruso in New York contributed to this report