“Professor Dershowitz will present oral arguments at the Senate trial to address the constitutional arguments against impeachment and removal,” said a statement on his Twitter account.

“He believes the issues at stake go to the heart of our enduring Constitution.”

With past clients including convicted sex offender Jeffrey Epstein, O.J. Simpson, film director Roman Polanski and Mike Tyson, Dershowitz is probably the best known lawyer to the stars in the US.

He will be part of a team with serious firepower headed by the White House’s discreet but uncompromising counsel Pat Cipollone.

Impeachment trial starts as watchdog says Trump broke law over Ukraine

Trump was impeached on charges of abuse of power and obstructing Congress.

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

The president insists he did nothing wrong, and he dismissed the trial anew on Thursday at the White House: “It’s totally partisan. It’s a hoax.”

The Government Accountability Office said on 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.

The 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.

Cipollone is behind the White House’s strategy of refusing to cooperate with Democratic investigators throughout the impeachment probe.

The White House has yet to announce the full team but confirms that Cipollone will be the lead lawyer, backed by Trump lawyer Jay Sekulow.