Asked if Bolton - Trump’s former national security adviser - should testify at Trump’s impeachment trial, Kelly said he supports calling witnesses.

President Donald Trump is denying that he told former National Security Adviser John Bolton that he wanted to withhold military aid from Ukraine until the country launched investigations into Joe Biden and his son, allegations that Bolton levies in his new book, according to a New York Times report.

But one of Trump’s former top aides told a Sarasota audience Monday evening that if the reporting on what Bolton wrote is accurate, he believes Bolton.

"If John Bolton says that in the book, I believe John Bolton," said retired Gen. John Kelly, who served as Trump’s chief of staff for 18 months.

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Kelly spoke Monday at the Van Wezel Performing Arts Hall as part of the Ringling College Library Association Town Hall lecture series. The general worked with Bolton during his time as chief of staff, which ended in early 2019. Kelly said Bolton is an honest person.

"Every single time I was with him … he always gave the president the unvarnished truth," Kelly said of Bolton, who has become a figure of intense interest in the impeachment inquiry.

According to the New York Times, Bolton writes in a book yet to be released that Trump personally told him he did not want to release nearly $400 million in military aid to Ukraine until the country investigated Democrats, including the former vice president and his son.

The House impeached Trump last year, alleging that the president abused his power by leveraging the military aid to try to benefit himself politically.

Trump denies ever tying the aid to the investigations.

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"I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens," Trump tweeted recently, adding: "If John Bolton said this, it was only to sell a book."

I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens. In fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book. With that being said, the...

— Donald J. Trump (@realDonaldTrump) January 27, 2020

Asked about the passages in Bolton’s book — which is scheduled to be released on March 17 — that appear to reinforce the impeachment allegations, Kelly said Monday evening that "John’s an honest guy. He’s a man of integrity and great character, so we’ll see what happens." Kelly ended his answer by saying he believes Bolton.

There are growing calls for Bolton to testify in the Senate impeachment trial, something GOP leaders have resisted. Kelly said he supports calling witnesses during the 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," Kelly said.

"So I think if there are people that could contribute to this, either innocence or guilt … I think they should be heard," Kelly said, adding: "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."

Kelly also said earlier in the day that the Ukraine aid should not have been held up.

"When the United States Congress gives the money to buy the equipment to give to this particular country, to not send it over there as fast as we can is not the right answer," Kelly said.