Washington CNN  — 

Former White House chief of staff John Kelly says he believes John Bolton’s allegation that President Donald Trump told the former national security adviser that US security aid to Ukraine was conditioned on an investigation of the President’s political rivals, adding that Bolton should be heard from.

“If John Bolton says that in the book I believe John Bolton,” Kelly said Monday night when asked about the leaked draft manuscript during remarks at the Ringling College Library Association Town Hall lecture series, according to the Herald Tribune of Sarasota, Florida.

Kelly said Bolton “always gave the president the unvarnished truth” and is a “man of integrity and great character.”

“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,” Kelly said.

“So I think if there are people that could contribute to this, either innocence or guilt … I think they should be heard. 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.”

Bolton’s allegations, contained in a draft manuscript first reported by The New York Times, have led to fresh calls from Democrats for Bolton to testify in Trump’s impeachment trial and added uncertainty to a vote, expected this week, to determine whether the Senate should subpoena for witnesses and documents.

A source with direct knowledge of the manuscript has told CNN the Times’ telling of Bolton’s account is accurate. The President, though, has denied claims he told Bolton aid to Ukraine was tied to an investigation of the Bidens.

Trump’s attempts to pressure Ukraine to investigate Hunter Biden and Joe Biden, his potential 2020 rival, are at the center of the President’s impeachment trial.

Trump has repeatedly made unfounded and false claims to allege that the Bidens acted improperly in Ukraine. There is no evidence of wrongdoing by either Joe or Hunter Biden.

Kelly, who left the White House under contentious circumstances in January 2019, has occasionally voiced criticisms of the Trump administration since leaving his post.

In October, the retired Marine Corps general said the President would not be in the middle of an impeachment process if he were still chief of staff, implying that White House advisers could have prevented it. He also said before he left the White House he advised Trump on hiring his replacement.

“I said, whatever you do — and we were still in the process of trying to find someone to take my place — I said whatever you do, don’t hire a ‘yes man,’ someone who won’t tell you the truth — don’t do that,” Kelly said at the time. “Because if you do, I believe you will be impeached.”

This story has been updated to include additional background information.