An attorney for John Bolton has pushed back against the White House’s assessment that his book manuscript contains classified material and asked for an expedited review of a chapter about Ukraine in case the former national security adviser is called to testify in the Senate impeachment trial.

The Jan. 24 email to the White House from Bolton’s lawyer, Charles Cooper, was in response to a letter from the National Security Council a day earlier warning that the manuscript contained “significant amounts” of classified material that could not be disclosed publicly.

“We do not believe that any of that information could reasonably be considered classified,” Cooper responded, according to a copy of the email he released Wednesday.

He added that Bolton is “preparing” for the possibility he could be called to testify in the ongoing Senate trial, writing that it was “imperative that we have the results of your review of that chapter as soon as possible.”

Cooper said in a statement Wednesday that he has not received a response to his “urgent request.”

The previously private exchange signals the likelihood of a protracted dispute over the contents of Bolton’s book and whether he could testify about his knowledge of President Trump’s activities related to Ukraine.

Revelations about the contents of his manuscript have intensified the debate on Capitol Hill about whether to call witnesses for the Senate trial. Trump has attacked his former adviser, tweeting Wednesday that Bolton wrote “a nasty & untrue book.”

The communication between Cooper and the White House occurred last week, just a few days before the New York Times published details from his manuscript, including Bolton’s claim that Trump told him in August that he was tying Ukrainian investigations of his political opponent to continuing foreign aid to that country.

The allegation is at the center of the impeachment trial unfolding on Capitol Hill — and has provoked the president’s wrath.

“Why didn’t John Bolton complain about this ‘nonsense’ a long time ago, when he was very publicly terminated,” Trump tweeted after returning from a raucous campaign rally in New Jersey on Tuesday. “He said, not that it matters, NOTHING!”

Bolton, who said he had resigned last September, even as Trump said he was fired, had clashed with the president on a range of issues during his 17-month tenure, including North Korea, Venezuela and Iran. He left office on Sept. 10, the day before frozen aid to Ukraine was released by the White House.

As the Senate impeachment trial turned to lawmaker questions to the House managers and Trump’s legal team Wednesday, Minority Leader Charles E. Schumer (D-N.Y.) addressed Bolton’s possible testimony in the first question, asking the managers if there was “any way to render a verdict in this case” without hearing from Bolton and other senior White House officials.

The dispute over classified information in Bolton’s account suggests there may be considerable hurdles to overcome before Bolton testifies or publishes his account.

In a Jan. 23 letter to Cooper, the White House official responsible for vetting manuscripts said Bolton’s book contained classified material, including some considered top secret.

The letter, written by Ellen J. Knight, the security council’s senior director for records, access and information security management, said Bolton would be breaking his nondisclosure agreement with the U.S. government if he published the book without deleting the classified material.

In her letter, Knight said her office would work with Bolton to “revise the manuscript” so he can “tell his story in a manner that protects U.S. national security.”

The letter indicates that Knight and Cooper had also spoken on the telephone the day before.

“The manuscript may not be published or otherwise disclosed without the deletion of this classified information,” she wrote.

Cooper had submitted the manuscript to the National Security Council for vetting on Dec. 30. In his letter accompanying the draft, addressed to Knight, he said that his client believed that no classified information was discussed.

“Ambassador Bolton has carefully sought to avoid any discussion in the manuscript of . . . classified information, and we accordingly do not believe that prepublication review is required,” Cooper wrote. “We are nonetheless submitting this manuscript out of an abundance of caution.”

A person familiar with the discussions, who spoke on the condition of anonymity because of the sensitivity of the dispute, said Bolton’s team expects a lengthy fight over the issue.

Legal experts said the White House might also challenge Bolton’s account — in a book or elsewhere — as a violation of executive privilege.

A number of White House officials, including Counsel Pat Cipollone, top national security lawyer John Eisenberg and acting chief of staff Mick Mulvaney, have not seen the manuscript, according to White House aides.