Washington (CNN) FBI Deputy Director Andrew McCabe has told FBI staff he is stepping down effective Monday -- a move that surprised even those expecting his March retirement, sources tell CNN.

McCabe was a central target of President Donald Trump's ire toward the FBI over its involvement in the investigation into potential collusion between his campaign and Russia during the 2016 election.

He was eligible to retire in March, but with his accumulated leave, he was able to step down earlier.

Trump learned about the departure Monday morning, a White House official told CNN. The President did not answer a reporter's question at the White House about McCabe's departure.

White House press secretary Sarah Sanders said Trump was not part of McCabe's choice to step down and that the White House had not been part of the decision.

Various sources described McCabe's departure as a mutual decision, while others said it was the result of pressure to step down. One source briefed on the matter said McCabe announced his decision to senior executives and portrayed it as his choice. The source disputed the characterization that McCabe was removed.

But a source familiar with the matter said FBI Director Christopher Wray told McCabe he is bringing in his own team, which he would not be a part of, and that it was McCabe's decision whether to stay at the FBI or leave.

FBI Assistant Deputy Director David Bowdich has been appointed as the bureau's acting deputy director.

Nonstop pressure

Trump has kept nonstop pressure on McCabe ever since he became acting director in May, using the longtime law enforcement official as a punching bag -- both publicly and privately -- to vent his frustrations about the FBI. In December, Trump tweeted "FBI Deputy Director Andrew McCabe is racing the clock to retire with full benefits. 90 days to go?!!!"

And in July 2017, Trump flatly asked why Attorney General Jeff Sessions had not fired McCabe yet.

"Why didn't A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got big dollars ($700,000) for his wife's political run from Hillary Clinton and her representatives," Trump wrote . "Drain the Swamp!"

His issue with McCabe stems from his wife's failed run for the Virginia state Senate in 2015. The Wall Street Journal reported that Dr. Jill McCabe received six contributions totaling $467,500 from then-Democratic Virginia Gov. Terry McAuliffe's political action committee.

In addition, campaign records show that the state Democratic Party, over which McAuliffe has great influence, made two other payments totaling $207,788 in September and October 2015. These donations all occurred before McCabe took over as deputy director of the FBI and before he would have had any oversight into the Clinton email investigation.

The story, which came out during the 2016 campaign, colored Trump's view of McCabe and led him, according to The Washington Post , to ask McCabe who he voted for in the 2016 election.

Trump, during a briefing with reporters earlier this month, denied asking that question, but went on to slam McCabe, who briefly served as Trump's acting FBI director after Trump fired James Comey in May.

"I don't think so. No. I don't think I did," Trump told reporters about asking who McCabe voted for.

McCabe, according to two Virginia campaign consultants -- one Republican, one Democratic -- with access to the Virginia campaign participation rolls, did not vote in the 2016 presidential general election but did vote in the 2016 Republican presidential primary.

Trump stands by his criticism of McCabe, Sanders said Monday, referring further questions to the FBI.

'The Russia fever'

Sessions communicated to FBI Director Christopher Wray, who was hand-picked by Trump and sworn in in August, that he needed a fresh start with his senior team at the FBI, a source familiar with the conversation has told CNN. Sessions specifically suggested McCabe and the bureau's top lawyer, James Baker, should go. Baker was reassigned late last year.

With his departure, McCabe joins a list of other top bureau officials who have stepped down in recent days as Wray assembles his own team. The departures of the FBI chief of staff and general counsel were also revealed this month

Sanders on Monday defended the pressure the President has placed on the FBI and Justice Department over the Russia investigation, telling CNN's Jim Acosta at the White House briefing that the administration has done "everything we can to be transparent."

"The only thing the President applied pressure to is to get it resolved so you guys and everyone else can focus on the things Americans actually care about: making sure everybody gets the Russia fever out of their system once and for all," she said.

This story is breaking and will be updated.