Senate Democrats on Sunday seized on a report on the draft of ex-national security adviser John Bolton’s new book to make their final pitch to "swing vote" Republicans who will decide on whether or not President Trump's Senate impeachment trial will include witnesses.

Bolton, along with Mick Mulvaney, the White House chief of staff, have been two witnesses coveted by Democrats who believe they both could provide first-hand evidence that Trump withheld U.S. aid from Ukraine for political gain and to damage Democrats and the Bidens.

WITNESS SWAP INVOLVING BIDEN AND BOLTON BEING CONSIDERED?

"The @NYTimes report suggests multiple top Trump Admin officials knew the facts and deliberately misled Congress and the American people," Sen. Chuck Schumer, D-N.Y., tweeted. The minority leader wrote that it is a "massive White House cover-up."

"All we need is four Republican Senators to get the truth," he tweeted late Sunday.

The three Republicans who may vote against the party line this week are Sens. Mitt Romney, Lisa Murkowski and Susan Collins. Democrats are also eyeing Sen. Lamar Alexander, R-Tenn, who the Hill reported has been tight-lipped on where he stands on the matter.

The New York Times, which said it received an unpublished manuscript of Bolton’s book, reported that its contents claim that Trump indeed ordered the Ukrainian aid to be held up until Kiev agreed to investigate the Bidens and other Democrats. The paper reported the Bolton passed around the manuscripts to close associates over the past few weeks.

Sarah Tinsley, a senior adviser to Bolton, told Fox News he had submitted a hard copy draft of his manuscript to the NSC several weeks ago for "pre-publication review," but insisted he had not shared it with anyone else. And, in a statement obtained by Fox News, Bolton attorney Charles Cooper lamented that the NSC review process had been "corrupted." He also provided his letter to the White House concerning the manuscript.

Bolton, who according to a witness had called Trump’s personal lawyer Rudy Giuliani a "hand grenade" and said a meeting about the White House's pressure on Ukraine tantamount to a "drug deal," has said he would be willing to testify if subpoenaed and has relevant information.

Trump on Monday attempted to refute the "The Room Where It Happened" manuscript’s reported claims and insisted that he never told Bolton that the aid was tied to the Biden investigation.

At the heart of the impeachment trial is Trump's July 25, 2019 call with Ukraine President Volodymyr Zelensky. Trump said the call was focused on corruption in Kiev and raised the Bidens as an example. Trump and Zelensky have both denied the Democrat claim that there was a quid pro quo. Trump called the entire impeachment process a political witch hunt.

Sen. Bernie Sanders, the 2020 Democratic hopeful, wrote on Twitter that the Senate "must hear from Bolton as a witness," and posted a link to the Times’ story.

Fiona Hill, a former top White House expert on Russia, testified in November that Bolton shared her concern about what she saw as a push to get Ukraine to conduct the investigations.

She testified in front of the House Intelligence Committee and recalled Bolton expressing his own concerns about the push and told her to tell National Security Council lawyer John Eisenberg that he does not want to be a part of this "drug deal."

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"He was saying that sarcastically, of course, I mean, just to be clear. Actually, he was angry, but he was also sarcastic. I mean — he wasn’t inferring that they were cooking up an actual drug deal in the War Room," she said.

Fox News' Gregg Re and Gillian Turner contributed to this report