President Trump said Tuesday that former national security adviser John Bolton "would know nothing about what we're talking about" if he testified in the Senate impeachment trial, adding that it will be "up to the lawyers" and the Senate to decide whether he appears.

Reality check: A number of witnesses told the House impeachment inquiry that Bolton was present in several meetings and conversations related to President Trump's decision to withhold military aid to Ukraine. Axios also reported in November that current and former administration officials believe Bolton was the most prolific note-taker at the top level of the White House.

Former National Security Council official Tim Morrison told impeachment investigators Bolton met privately with the president in August to convince him to release nearly $400 million in frozen military aid to Ukraine.

told impeachment investigators Bolton met privately with the president in August to convince him to release nearly $400 million in frozen military aid to Ukraine. Former White House official Fiona Hill recounted an episode during which Bolton told her, “I am not part of whatever drug deal [EU Ambassador Gordon] Sondland and [acting chief of staff Mick] Mulvaney are cooking up,” and asked her to relay that message to White House lawyers.

recounted an episode during which Bolton told her, “I am not part of whatever drug deal [EU Ambassador Gordon] Sondland and [acting chief of staff Mick] Mulvaney are cooking up,” and asked her to relay that message to White House lawyers. Bolton's lawyer confirmed in November he was a "part of many relevant meetings and conversations" that would be significant to the impeachment inquiry.

The state of play: Bolton said on Monday that he would testify in Trump's impeachment trial if the Senate subpoenaed him. However, that would require four GOP senators to vote with Democrats to call him as a witness, and it's unclear whether enough moderate Republicans would be willing to break ranks.

Senate Majority Leader Mitch McConnell said Tuesday he plans to move forward on approving rules for the trial without negotiating with Democrats.

McConnell has expressed no interest in subpoenaing Bolton, but Minority Leader Chuck Schumer will still likely bring votes on witnesses after each side makes its opening arguments.

Of note: Trump tweeted in November about Bolton and his dealings with Ukraine, stating, "John Bolton is a patriot and may know that I held back the money from Ukraine because it is considered a corrupt country, & I wanted to know why nearby European countries weren’t putting up money also."

Go deeper: Key GOP senators don't want to subpoena John Bolton