President Donald Trump announced that he has asked National Security Adviser John Bolton to resign, noting that he “strongly disagreed with many” of Bolton’s suggestions “as did others in the administration.”

“I thank John very much for his service. I will be naming a new National Security Advisor next week,” Trump tweeted on Tuesday.

The tweet came one hour after the White House press office said Bolton was scheduled to appear at a Tuesday press briefing alongside Secretary of State Mike Pompeo and Treasury Secretary Steve Mnuchin.

When asked during the briefing whether he and Mnuchin were surprised that Bolton was fired, given that he was supposed to appear alongside them, Pompeo said, “I’m never surprised.”

Bolton in a tweet minutes after Trump’s tweet said he offered to leave his post voluntarily.

“I offered to resign last night and President Trump said, ‘Let’s talk about it tomorrow,'” he tweeted.

Bolton reiterated the point that he offered to resign to Fox News on Tuesday.

His resignation letter to Trump, dated Tuesday, was short and to the point with Bolton writing: ‘I hereby resign, effective immediately, as Assistant to the President for National Security Affairs. Thank you for having afforded me this opportunity to serve our country.”

The White House is already discussing potential candidates to replace Bolton. There are at least 10 names being circulated and there does not appear to be a shortlist at this time.

Trump said he will make a decision next week but given the President’s unpredictable nature, sources warn that he could choose someone who is not under discussion right now.

So far, President Trump has had three national security advisers — Bolton, Michael Flynn and H.R. McMaster. He has summarily fired a secretary of state, Rex Tillerson, by tweet after undercutting the former ExxonMobil CEO for months.

Secretary of Defense James Mattis resigned, reportedly in frustration over Trump’s decision to pull out of Syria.

The President has also churned through two Homeland Security secretaries, John Kelly and Kirstjen Nielsen, and a National Security Agency director, Mike Rogers.

He’s lost a deputy national security adviser, K.T. McFarland and an ambassador to the UN, Nikki Haley. Director of National Intelligence Dan Coats and his deputy, Sue Gordon, left their posts last month.

Bolton’s departure comes amid tensions with Iran escalating in the Persian Gulf, North Korea continues to develop its weapons capabilities, arms control experts are warning of a potential nuclear arms race with Russia and trade tensions with China are intensifying, while Trump is discussing a drawdown of forces in Afghanistan.

White House deputy press secretary Hogan Gidley told reporters that Charles Kupperman is the acting national security adviser.

“John Bolton’s priorities and policies just don’t line up with the President’s and any sitting president has the right to put someone in that position that can carry out his agenda. That became no longer tenable so the President made a change,” Gidley told reporters.

He claimed there was “no one issue” that led to Bolton’s firing, and referred reporters to the forthcoming briefing for more information.

One of the factors that prompted Trump to fire Bolton was the concern inside the White House that Bolton’s aides were making it sound as though Vice President Mike Pence had opposed the Taliban meeting at Camp David, according to two senior administration officials. One official pointed to Pence’s tweet saying he would have supported such a move.

Pompeo acknowledged on Tuesday that he disagreed with Bolton “many times.”

“That’s for sure,” he said, but added he disagrees with others as well.

Bolton was initially brought into the administration last year to replace HR McMaster partly due to his hawkish position on Iran — supporting Trump’s exit from the Iran nuclear deal — but he soon began to clash with the President’s vision for diplomacy in North Korea and most recently on Afghanistan.

President Trump also felt like Bolton wasn’t a forceful enough advocate for him in the media — and that when he did make appearances, he wasn’t convincing enough, since it was evident he didn’t believe in some of Trump’s foreign policy goals, a senior administration official said.