Alan Dershowitz, the Harvard Law emeritus professor who recently joined President Donald Trump’s legal team, on Sunday distanced himself from a response by two White House lawyers to House Democrats’ impeachment case against the president, noting that he did not sign on to the document.

“I didn’t sign that brief,” Dershowitz said in an interview on ABC News’ “This Week.” “I didn’t even see the brief until after it was filed. That’s not part of my mandate. My mandate is to determine what is a constitutionally authorized criteria for impeachment.”

Dershowitz is one of four lawyers who were selected personally by Trump and announced Friday as new members of the president’s legal team. The others are former Florida Attorney General Pam Bondi and former independent counsels Robert Ray and Kenneth Starr.

Dershowitz’s comments come as both sides preview their arguments for Trump’s impeachment trial, which begins in earnest this week and is only the third such trial in U.S. history.

House Intelligence Committee Chairman Adam Schiff, the lead impeachment manager, said Sunday that Democrats will be “fighting for a fair trial” and pushed back against critics who have argued that the House should have done more to enforce its subpoenas before voting to impeach Trump.

“The reality is, because what the president is threatening to do is cheat in the next election, you cannot wait months and years to be able to remove that threat from office,” Schiff said on “This Week.”

Trump has urged the Senate to dismiss the charges against him.