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President Donald Trump says John Bolton is only trying “to sell a book” after it emerged that the former national security adviser will claim in his forthcoming memoir that the U.S. president withheld military aid to the Ukraine government to get it to investigate Joe Biden and his son.

In a trio of tweets just after midnight on Sunday, Trump lashed out at reports that Bolton’s new book contains claims that last August the U.S. president told his then-national security that he wanted to continue freezing $391 million in security assistance to Ukraine until officials there helped with investigations into Democrats, including the Bidens.

“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,” Trump tweeted.

The contents of Bolton’s book, “The Room Where It Happened; A White House Memoir,” which is not set to be released until March, were reported by the New York Times, but have subsequently been confirmed by multiple media outlets.

But Trump and the White House should not have been surprised by the claims in Bolton’s book: a copy of the manuscript was sent to the White House last month.

The Ukraine scandal is at the heart of the impeachment engulfing Washington, but Trump and his legal team have strenuously denied there was a quid pro quo in the exchanges with Ukranian President Volodymyr Zelensky.

But the reports about the contents of Bolton’s book sparked an immediate reaction from Democrats on Capitol Hill on Sunday night, with all seven House managers calling for all senators to insist that Bolton be called as a witness and provide his notes and other relevant documents.

“Americans know that a fair trial must include both the documents and witnesses blocked by the President — that starts with Mr. Bolton,” the impeachment managers said in a statement.

Sen. Chuck Schumer, the Senate’s top Democrat and Speaker of the House Nancy Pelosi, issued the same call.

Trump returned to topic once again on Monday, tweeting that the “Democrat-controlled House never even asked John Bolton to testify. It is up to them, not up to the Senate!”

However, the House did in fact invite Bolton to testify in November, but he refused to attend. Earlier this month Bolton said he had changed his mind and was now willing to participate in the process.

Bolton, who left the White House on acrimonious terms in September, has already indicated he is willing to testify despite Trump’s blanket ban on aides cooperating with the investigation.

Trump’s high-profile legal team will continue its defense of the president on Monday, after a rare Saturday session of the Senate saw them lay out the broad outlines of their defense.