House impeachment manager Adam Schiff (D-CA) expressed no regrets when asked if he could’ve done anything differently in the Senate impeachment trial during an interview on CBS’ “Face the Nation” Sunday morning.

When CBS’ Margaret Brennan asked Schiff for his response to Sen. Lisa Murkowski’s (R-AK) statement regarding her vote against calling witnesses to testify — which included calling the articles of impeachment flawed and saying that the partisan nature of this impeachment gets in the way of a fair trial in the Senate — Schiff said that Murkowski and other senators are “not mere spectators here” and that “it’s up to the senators to make it a fair trial.”

“It is within their power to make it a fair trial with four votes, with four courageous senators saying, ‘no, we’re going to demand a fair trial no matter what this president may say,'” Schiff said. “There would have been a fair trial. There would have been witnesses and testimony. So it’s not as if she was powerless to do something about this.”

Asked whether there is anything he would have done differently, Schiff said “there’s nothing that I can see that we could have done differently because as the senators have already admitted, we proved our case.”

Schiff went on to argue that just because the president’s lawyers have said that “the process in this impeachment was different than in Nixon and Clinton,” that is “not an excuse that should be used by any senator for not fulfilling their obligation to hold a fair trial.”

“They’re not spectators. They have control over the proceedings. And they could have insisted on witnesses and documents and for whatever reason, chose not to,” Schiff said. “And for those who would say, well, let’s let the voters decide when the President is trying to cheat in that very election — and they don’t want the voters to have the full information — they want the president to continue to be able to cover it up. That’s just completely unsatisfactory.”

Watch Schiff’s remarks below: