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."

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.