Mr Mueller is investigating whether Mr Trump's actions, including Mr Comey's dismissal, constitute obstruction of justice.
Trump had repeatedly criticized McCabe as biased, pressing Sessions to take action against him.
The recommendation to fire McCabe didn't come from the Attorney General, it came from F.B.I. disciplinary officials making his termination less about politics and more about maintaining the integrity of the F.B.I. after abuses by McCabe, James Comey, Peter Strzok, and Lisa Page came to light past year.
Trump then took a shot at James Comey, McCabe's former boss whom Trump fired in May 2017, declaring him to be "sanctimonious" and that he made "McCabe look like a choirboy". If there is doubt that the timing of Mr. McCabe's dismissal was driven by political vengeance, Mr. Trump does everything he can to prove the worst with his own sordid words.
The media outreach came at a time when McCabe said he was facing public accusations of partisanship and followed reports that his wife, during a run for the state Senate in Virginia, had received campaign contributions from a Clinton ally. How many lies? How many leaks?
A spokesman for the inspector general's office declined to comment.
Friday's move by Sessions comes after FBI officials concluded McCabe should be fired for allegedly misleading internal investigators about his role two years ago in allowing an FBI spokesman and FBI attorney to disclose information about the agency's Clinton Foundationinvestigation to a reporter. "This distortion of the process begins at the very top, with the president's repeated offensive, drive-by Twitter attacks on Mr. McCabe", Mr. Bromwich said late Friday. "And they can judge for themselves who is honourable and who is not".
According to House Intelligence Committee chair Devin Nunes' infamous memo, McCabe is one of the individuals who willfully deceived the FISA court about both the dossier's provenance and its veracity.
Nevertheless, the president expounded on Twitter about the importance of pushing McCabe out.
The firing will only stoke the political fires around the Mueller investigation of Trump.
The President has crusaded for months against McCabe, who is a crucial corroborating witness to Trump's attempts to stymie the F.B.I.'s investigation of his campaign's ties to Russian Federation. Mr. Comey was sacked last spring, and the revelation of his conversations with Mr. Trump helped lead to the special counsel's appointment.
McCabe was sacked Friday night, just before his scheduled retirement after 21 years at the Federal Bureau of Investigation and before his lifetime pension went into effect. McCabe was sacked two days before his retirement date on Sunday. "But headlines like this are not the way out".
Former FBI officials tell CNN that McCabe could also lose out on future health care coverage in his retirement if he were to be fired before he turned 50, and the firing could be subject to litigation. "America will triumph over you".
Former Attorney-General Eric Holder wrote, "Analyse McCabe firing on two levels: the substance and the timing".
Many at the bureau were saying, "This is insane. People could disagree about the decisions I made. but the fact is this is not a leak".
U.S. Department of Justice building in Washington, D.C. Those familiar with McCabe's side of the story say he was authorized to talk to reporters.