House impeachment manager Adam Schiff (D-CA) said on Monday morning that Republican senators are in a bind after the New York Times published allegations of former National Security Adviser’s book, which gave a firsthand account of President Donald Trump’s involvement in the pressure campaign on Ukraine.

“At the end of the day, Alisyn, this the test for these senators,” Schiff told CNN’s “New Day” anchor Alisyn Camerota. “They’ve taken an oath to be impartial. They’ve just learned there’s a key witness going to the heart of the allegations.”

“The question they have to answer is: Do they want to hear the truth? Do they want to cross-examination John Bolton?” the Democratic lawmaker continued.

Schiff said that he and the rest of the Democrats will push Republicans to allow testimony from Bolton, who has offered to testify in the Senate impeachment trial if the chamber issued a subpoena.

“And I think all the senators are now really hard-pressed to turn him away,” the impeachment manager added.

According to the Times, Bolton wrote that Trump had told him he wanted to withhold the congressionally approved aid until Ukraine had given him materials on their Russia investigation as it related to Joe Biden and Hillary Clinton.

Republican senators have voted to shoot down Senate Minority Leader Chuck Schumer’s (D-NY) attempts to allow Bolton and other top Trump administration officials to testify. However, GOP sources told Politico and Axios that Bolton’s bombshell allegations may have thrown the senators’ resistance against witnesses into question.

Watch Schiff below: