A new reported claim by former National Security Adviser John Bolton "blasts another hole" in President Trump's impeachment defense and sets the stage for a tough vote for Republicans in the Senate trial, Rep. Adam Schiff said Monday.

The Calfornia Democrat, who serves as the House's lead manager in presenting the impeachment case to the Senate trial, responded on CNN to the New York Times report that in his forthcoming book, Bolton will claim that Trump explicitly linked a hold on Ukraine aid to an investigation of Joe and Hunter Biden. Schiff said given the claim, senators must be able to hear from Bolton directly.

"This would be another witness that would corroborate in very direct terms, if this report is accurate, that the president told him unequivocally he was holding up the money until Ukraine did these investigations. It completely blasts another hole in the president’s defense," said the House Intelligence Committee chairman, adding that Bolton's claim is backed up by previous testimony in the House by EU Ambassador Gordon Sondland.

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Trump fired back on Twitter on Sunday to refute Bolton's claims, saying he "NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens." Trump went on to accuse Bolton of trying to "sell a book," noting that Bolton did not complain publicly or privately about the aid holdup "at the time of his very public termination."

Democrats are expected to call for testimony from Bolton, with a majority vote needed in the Republican-controlled Senate to allow additional witnesses.

"For every senator, Democrat and Republican, I don’t know how you can explain that you wanted a search for the truth in this trial and say you don’t want to hear from a witness who had a direct conversation about the central allegation in the articles of impeachment," said Schiff.

"All of these senators, on March 17th when this book comes out, are going to be asked if they don’t support calling him as a witness, why didn’t you want to hear from him when he could have given you information before you rendered your verdict? I would just not want to be in a position of having to answer that question."

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The Times further claimed Bolton had shared a manuscript of his forthcoming book with "close associates" -- prompting Bolton's team to deny the claim, and assert that the National Security Council's [NSC's] review process of pending manuscripts is "corrupted" and prone to leaks.

A "pre-publication review" at the NSC, which functions as the White House's national security forum, is standard for any former government officials who held security clearances and publicly write or speak publicly about their official work. The review typically would focus on ferreting out any classified or sensitive material in advance of publication, and could take from days to months.

Fox News' Gregg Re contributed to this report.