The White House impeachment legal defense team is taking shape as the Senate trial is set to begin next week, adding lawyers Alan Dershowitz, Kenneth Starr and Robert Ray to the group, according to a source familiar with the plans.

The source tells TIME that White House counsel Pat Cipollone and Donald Trump’s personal lawyer Jay Sekulow will take the lead on the defense. But the addition of constitutional law expert Dershowitz, former independent counsel Starr —whose work led to the impeachment of President Bill Clinton— and Ray, who succeeded Starr at the Office of the Independent Counsel under Clinton, adds three veteran lawyers to the team with some star power.

“While Professor Dershowitz is non partisan 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,” read a statement tweeted on Friday by Dershowitz, who has occasionally advised Trump. “He is participating in this impeachment trial to defend the integrity of the Constitution and to prevent the creation of a dangerous constitutional precedent.”

The members of the legal defense team, which is also aided by Cipollone’s deputies Patrick Philbin and Michael Purpura, have been preparing for what they hope to be a speedy trial. A senior administration official told reporters earlier this week that it is “extraordinarily unlikely” that the trial runs beyond two weeks, in part because the administration doesn’t want additional witnesses called before the Senate.

“We don’t think that there’s going to be any need for witnesses in this trial,” the senior administration official said. “We think, at that point, they wouldn’t need to hear anything else because this is an extraordinarily weak case for the House managers.”

If Democrats are able to wrangle enough votes in the Senate to call former national security adviser John Bolton to testify, Trump’s legal defense may put up a fight over executive privilege. “It would be extraordinary to have the national security advisor testifying about his communications directly with the President about foreign policy and national security matters,” the senior administration official said on the call with reporters.

Trump’s legal team is prepared to defend him by advancing arguments that there was no crime laid out in the abuse of power impeachment article, and there was no obstruction of Congress based on a strong view of executive power. (Many legal scholars think an impeachable offense does not need to be a specific crime.)

“These are the weakest articles of impeachment that have ever been passed in any presidential impeachment. They state no violation of a crime, no violation of any law,” said the senior administration official. “The idea that it is obstruction of justice, obstruction of Congress for the President to assert constitutionally grounded privileges that protect the separation of powers is absurd.”

The Senate impeachment trial is set to begin in earnest on January 21.

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Write to Tessa Berenson at tessa.berenson@time.com.