Washington CNN  — 

Lead House impeachment manager Rep. Adam Schiff argued Monday that Republican senators cannot say they want “a search for the truth” in President Donald Trump’s impeachment trial if they don’t vote to subpoena former national security adviser John Bolton.

On Sunday, The New York Times, citing multiple people’s descriptions of an unpublished draft manuscript by Bolton, reported Trump in August told his then-national security adviser that he wanted to continue holding military aid to Ukraine until the country helped with investigations into Democrats, including former Vice President Joe Biden. Trump’s purported statement, as described by Bolton, would directly tie the US military aid freeze with the President’s requests that Ukraine announce investigations into his political rivals – undermining a key pillar of the President’s impeachment defense that the two circumstances are unrelated.

The news has placed new pressure on Senate Republicans to allow witnesses, including Bolton, to testify in the trial.

“I think for the senators, and I’m just not talking about the four that been so much the focus of attention, 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,” Schiff told CNN’s Alisyn Camerota on “New Day” Monday.

The new revelations change the Senate trial “very dramatically,” said Schiff, the House Intelligence Committee chairman.

Republicans and Democrats have so far been divided along party lines on the issue of including witnesses in Trump’s trial, and Democrats have been trying to peel off four GOP senators in order to subpoena witnesses like Bolton or acting chief of staff Mick Mulvaney. Among the swing votes Democrats are eyeing are Sens. Mitt Romney of Utah, Susan Collins of Maine, Lisa Murkowski of Alaska and Lamar Alexander of Tennessee.

“All of these senators on March 17, when (Bolton’s) 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?’” Schiff said. “I just would not want to be in a position of having to answer that question.”

The President has denied Bolton’s claims in a series of late night tweets, writing that he “NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens.” There is no evidence of wrongdoing by Biden or his son Hunter.

Schiff wouldn’t say if the Democratic-led House would subpoena Bolton if the Senate doesn’t.

“The reality is the senators ought to hear this witness firsthand,” he told Camerota.

The chairman said he hasn’t yet seen the manuscripts reported on by the Times, and did not say whether his committee would try to obtain copies of them.

“You know what I think is more important than the manuscript, and I don’t have an answer for that question right now, are John Bolton’s notes,” he said. “These notes took place while the events were happening, while they were fresh in his mind. Those in many respects are more important than the manuscript.”

This story has been updated with additional information.