Democrats are reiterating their demands for witnesses to appear before the Senate’s impeachment trial after The New York Times reported Sunday that a draft outline of former national security adviser John Bolton’s book includes his recollection that President Donald Trump tied withholding aid from Ukraine to the country investigating his political rival.

The draft outline reportedly described Trump telling Bolton in August that he wanted to continue freezing almost $400 million in congressionally approved military aid to Ukraine until officials there agreed to help investigate former Vice President Joe Biden and his son Hunter. Tying the two together would reveal that Trump attempted a quid pro with a foreign government, which Democrats have been saying he did for months.

The House impeached Trump in December, and his trial began in the Senate earlier this month. House impeachment managers spent three days last week presenting their opening argument﻿ to senators, while Trump’s defense team spent a couple of hours on Saturday giving their argument.

The Democratic House impeachment managers were some of the first to respond to the Times report, releasing a statement demanding Bolton be called as a witness in the trial.

“There is no defensible reason to wait until his book is published, when the information he has to offer is critical to the most important decision Senators must now make ― whether to convict the President of impeachable offenses,” the statement read.

House Impeachment Managers: "There can be no doubt now that Mr. Bolton directly contradicts the heart of the President's defense and therefore must be called as a witness at the impeachment trial of President Trump." — Kyle Griffin (@kylegriffin1) January 27, 2020

House Speaker Nancy Pelosi (D-Calif.), who led Democrats through the impeachment inquiry, said Senate Republicans refusing to call on Bolton and other key witnesses to testify amounts to choosing a cover-up over the Constitution.

Amb. Bolton reportedly heard directly from Trump that aid for Ukraine was tied to political investigations.



The refusal of the Senate to call for him, other relevant witnesses, and documents is now even more indefensible.



The choice is clear: our Constitution, or a cover-up. https://t.co/HBW82ObvOl — Nancy Pelosi (@SpeakerPelosi) January 27, 2020

The draft outline gives a view of what Bolton might say if called as a witness, according to the Times. Bolton has said that he would testify before senators if subpoenaed, but Senate Republicans have effectively stonewalled efforts to call any witnesses or bring any additional evidence for review in the trial.

The upper chamber will vote on whether to consider witnesses and additional evidence after a period of questioning by senators from both parties.

In order to subpoena new witnesses in the trial, Democrats need to sway at least four Republican senators to support an initial vote on including more evidence. Three Republicans have shown some level of interest in potentially voting in favor of doing so: Mitt Romney of Utah, Susan Collins of Maine, and Lisa Murkowski of Alaska.

Senate Minority Leader Chuck Schumer (D-N.Y.), who has led the charge in trying to bring witness testimony to the impeachment trial, reiterated his demands in response to the Times report.

“John Bolton has the evidence,” Schumer tweeted Sunday night. “It’s up to four Senate Republicans to ensure that John Bolton, Mick Mulvaney, and the others with direct knowledge of President Trump’s actions testify in the Senate trial.”

John Bolton has the evidence.



It’s up to four Senate Republicans to ensure that John Bolton, Mick Mulvaney, and the others with direct knowledge of President Trump’s actions testify in the Senate trial.https://t.co/JbazBaYdRU — Chuck Schumer (@SenSchumer) January 26, 2020

Other senators also spoke up in the wake of the report. Sen. Chris Coons, a Delaware Democrat who often works with Republicans, pressured his GOP colleagues to also call for witness testimony.

“Congressman Schiff wisely cautioned all Senators just last week that ― eventually ― the full truth about the President’s actions will come out,” Coons said. “It’s our duty to ensure the truth comes out before the ongoing impeachment trial concludes.”

.@ChrisCoons puts out a statement tonight on the new Bolton reporting from the @nytimes. Coons, who frequently works across the aisle, puts pressure on his GOP colleagues to call for witness testimony: pic.twitter.com/Nl29t96a8i — Elizabeth Landers (@ElizLanders) January 27, 2020

Sen. Amy Klobuchar (D-Minn.) echoed Coons’ calls for the GOP to demand witnesses, telling the Times that “they should all be calling for witnesses” and noting Romney has done so already.

Sen. Doug Jones (D-Ala.) suggested that if the Senate couldn’t hear from Bolton himself, they should get a subpoena for his book.

The Senate needs to hear from Bolton. The American people deserve to hear from Bolton. If we can’t get Bolton let’s get a subpoena for the book!#subpoenathebook#ImpartialJustice https://t.co/vDCVMORMtI — Doug Jones (@DougJones) January 27, 2020

Liza Hearon contributed to this article.