Former White House Chief of Staff John Kelly said Monday he would believe that President Donald Trump sought to make U.S. military aid to Ukraine conditional on investigations — if former White House National Security Advisor John Bolton did indeed make the claim in his forthcoming book.

“If John Bolton says that in the book I believe John Bolton,” retired Gen. Kelly said during a lecture at a Ringling College Library Association town hall event in Sarasota, Florida, reports the Herald Tribune.

“Every single time I was with him… he always gave the president the unvarnished truth,” Kelly said of Bolton, whom he worked with for several months at the White House. “John’s an honest guy. He’s a man of integrity and great character, so we’ll see what happens.”

On Sunday, the New York Times first reported the alleged details in Bolton’s book, prompting suspicions that he, his publisher, or someone within the National Security Council leaked its contents to boost pre-order sales. The upcoming memoir went on sale for preorders at Amazon.com shortly after the Times’ report. Bolton has denied coordinating with the newspaper.

On the subject of the ongoing Democrat impeachment effort, Kelly said he believes additional witnesses should be called to testify in the Senate trial.

“I mean, half of Americans think this process is purely political and shouldn’t be happening ,but since it is happening, the majority of Americans would like to hear the whole story,” he said.

“So I think if there are people that could contribute to this, either innocence or guilt… I think they should be heard,” he added. “I think some of the conversations seem to me to be very inappropriate, but I wasn’t there. But there are people that were there that ought to be heard from.”

The Times’ report has reignited calls from Democrats to hear from Bolton in the Senate trial, though top Republicans continue to be dismissive of the idea — instead proposing that his manuscript be subpoenaed instead.

“I want to see what’s in the manuscript,” Sen. Lindsey Graham (R-SC), chairman of the Senate Judiciary Committee, told reporters on Monday. “Let’s see what’s in the manuscript, let’s see if it’s relevant, and if it is, I’ll make a decision about Bolton.”

The development has also prompted moderate Republicans — and possible impeachment swing votes — such as Sens. Mitt Romney (R-UT), Susan Collins (R-ME), and Lisa Murkowski (R-AK) to signal further interest in a Bolton testimony.

“I think with the story that came out yesterday, it’s increasingly apparent it would be important to hear from John Bolton,” Romney told reporters. “I, of course, will make a final decision on witnesses after we’ve heard from not only the prosecution but also the defense. But I think at this stage it’s pretty fair to say that John Bolton has a relevant testimony to provide to those of us who are sitting in impartial justice.”

In a separate statement, Murkowski said she was “curious” what the former Trump official had to say about the recent alleged revelations.

“I stated before that I was curious as to what John Bolton might have to say. From the outset, I’ve worked to ensure this trial would be fair and that members would have the opportunity to weigh in after its initial phase to determine if we need more info,” she said. “I’ve also said there is an appropriate time for us to evaluate whether we need additional information —that time is almost here. I look forward to the White House wrapping up presentation of its case.”

On Monday, President Trump denied the reported claims in an Oval Office meeting with Israeli Prime Minister Benjamin Netanyahu, calling the allegations unequivocally “false.”