Attorneys John Bolton, President Trump's former National Security Adviser, are in discussions with House committees about the possibility of giving a deposition in their impeachment investigations, according to CNN.

!!! John Bolton’s lawyers have consulted with the impeachment inquiry committees about a possible deposition. @kylieatwood — Shimon Prokupecz (@ShimonPro) October 25, 2019

Bolton, who some speculated was the original "first-hand" source of the whistleblower complaint which launched the impeachment inquiries, was fired after President Trump says he "disagreed strongly with many of his suggestions."

....I asked John for his resignation, which was given to me this morning. I thank John very much for his service. I will be naming a new National Security Advisor next week. — Donald J. Trump (@realDonaldTrump) September 10, 2019

According to sources, while Trump had been growing displeased with Bolton's belligerent recommendations and overall demeanor (recall "Bolton 'Deep in His Heart' Believes Trump Is a 'Moron,' Former Aide Claims"), the tipping point happened when Bolton expressed his displeasure with Trump's impromptu invitation of the Taliban to Camp David on the week of the Sept 11 anniversary, a peace overture which as we reported over the weekend, collapsed in the last moment.

The New York Times suggested on Thursday that "Among the star witnesses who could deliver explosive public testimony in front of live television cameras could be John R. Bolton, the president’s former national security adviser, who has been described in testimony as alarmed by what appeared to be pressure on the Ukrainians by Mr. Trump and his allies."

Earlier this month, the Times also reported that Bolton was 'so alarmed' by efforts to encourage Ukraine to investigate the Bidens over allegations of corruption that he told an aide, Fiona Hill, to alert White House lawyers. Hill told House investigators that Bolton got into a heated confrontation on July 10 with Trump's EU ambassador, Gordon D. Sondland, who was working with Trump attorney Rudy Giuliani to investigate Democrats. Hill said that Bolton told her to notify the top attorney for the National Security Council about the 'rogue' effort by Sondland, Giuliani and acting White House chief of staff Mick Mulvaney.

"I am not part of whatever drug deal Sondland and Mulvaney are cooking up," Bolton apparently told Hill to tell the lawyers.

It was not the first time Mr. Bolton expressed grave concerns to Ms. Hill about the campaign being run by Mr. Giuliani. “Giuliani’s a hand grenade who’s going to blow everybody up,” Ms. Hill quoted Mr. Bolton as saying during an earlier conversation. The testimony revealed in a powerful way just how divisive Mr. Giuliani’s efforts to extract damaging information about Democrats from Ukraine on President Trump’s behalf were within the White House. Ms. Hill, the senior director for European and Russian affairs, testified that Mr. Giuliani and his allies circumvented the usual national security process to run their own foreign policy efforts, leaving the president’s official advisers aware of the rogue operation yet powerless to stop it. -NYT

When Hill confronted Sondland, he told her that he was 'in charge' of Ukraine, "a moment she compared to Secretary of State Alexander M. Haig Jr.’s declaration that he was in charge after the Ronald Reagan assassination attempt, according to those who heard the testimony," according to the Times.