President Donald Trump went after John Bolton, his former national security adviser, in a series of Wednesday-morning tweets.

He called Bolton's coming memoir "nasty & untrue" and said that had he listened to Bolton, "we would be in World War Six by now."

The New York Times on Sunday reported that Bolton's coming book undercut a big part of Trump's defense against impeachment, saying that Trump explicitly linked Ukraine military aid to his requests for investigations into political rivals.

Republicans are deliberating over whether to call Bolton to testify in Trump's Senate impeachment trial.

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President Donald Trump excoriated John Bolton, his former national security adviser, on Twitter on Wednesday as Republican senators considered whether to call on Bolton to testify in the president's Senate impeachment trial.

Trump ripped into Bolton for writing what he described as a "nasty & untrue book," referring to Bolton's coming memoir.

The president, who has often said he hires only the "best people," also suggested "we would be in World War Six by now" if he had listened to Bolton while he was still national security adviser.

"For a guy who couldn't get approved for the Ambassador to the U.N. years ago, couldn't get approved for anything since, 'begged' me for a non Senate approved job, which I gave him despite many saying 'Don't do it, sir,' takes the job, mistakenly says 'Libyan Model' on T.V., and many more mistakes of judgement, gets fired because frankly, if I listened to him, we would be in World War Six by now, and goes out and IMMEDIATELY writes a nasty & untrue book. All Classified National Security. Who would do this?" Trump tweeted.

Trump then retweeted two of his own tweets from hours earlier. "Why didn't John Bolton complain about this 'nonsense' a long time ago, when he was very publicly terminated," Trump said in the first one. "He said, not that it matters, NOTHING!"

"No matter how many witnesses you give the Democrats, no matter how much information is given, like the quickly produced Transcripts, it will NEVER be enough for them," he said in the second retweet. "They will always scream UNFAIR. The Impeachment Hoax is just another political CON JOB!"

Trump's flurry of attacks came after new information seemed to raise the chances that senators might call on Bolton to testify in the impeachment trial.

The New York Times reported on Sunday that the former national security adviser's forthcoming book accused Trump of explicitly linking Ukraine military aid to requests for investigations into the president's political rivals. Such testimony would be the strongest evidence yet linking Trump to a so-called quid pro quo of congressionally approved military aid in exchange for investigations that could benefit Trump politically. Bolton. AP Photo/Alex Brandon

Bolton left his position as national security adviser in September, one day after the House launched three investigations into Trump's Ukraine dealings. The White House and Bolton have publicly sparred over whether he was fired or resigned.

House impeachment investigators invited Bolton to voluntarily testify in the fall, but he declined. Bolton said he would do so only if he was subpoenaed and if a court ruled he should comply over orders from the White House — which has moved to block current and former officials from testifying.

In early January, however, Bolton said he would testify if subpoenaed by the GOP-controlled Senate. Democrats have considered Bolton a potentially crucial witness given other testimony that signaled he had strong reservations about the efforts to urge Ukraine to announce investigations into Trump's rivals.

Trump's legal team concluded opening arguments in the Senate impeachment trial on Tuesday.

Senators will now have 16 hours for asking House impeachment managers and Trump's legal team questions before voting on whether to call for witnesses and further evidence. According to The Wall Street Journal, Senate Majority Leader Mitch McConnell on Tuesday night said he might not have enough votes to block witnesses from testifying.