When John Bolton’s departure from the Trump administration was announced Tuesday, it came as an abrupt end to the tenure of the president’s third national security adviser in as many years. Hours before Bolton was scheduled to appear at a White House press conference with Secretary of State Mike Pompeo and Treasury Secretary Steve Mnuchin, Trump announced on Twitter that “his services are no longer needed at the White House.” 

Trump said he had asked for Bolton’s resignation on Sept. 9, a Monday, which was given to him the next morning.

“I disagreed strongly with many of his suggestions, as did others in the administration … I thank John very much for his service,” Trump wrote.

Bolton, meanwhile, claimed he had offered to resign Monday evening but was told by Trump, “Let’s talk about it tomorrow.”

Brought on as national security adviser in March 2018, Bolton seemed ideologically aligned with the president in his criticism of international organizations — such as the International Criminal Court — and his disdain for the 2015 Iran nuclear deal brokered by the Obama administration. But Bolton clashed with the president on other issues, like whether to pull U.S. forces out of Syria, how best to negotiate with North Korea, how to deal with Russia (“We negotiate with Russia at our peril,” he wrote in a 2017 op-ed, after the president’s meeting with Russian president Vladimir Putin at the G20 summit) and, more recently, peace talks with the Taliban.

“In terms of style, Bolton suits Trump really well: the bombastic [style], the Fox News, the in-your-face shouting matches. In terms of substance, they’re on opposite pages,” DePaul political science professor Scott Hibbard said. “Trump liked his style, liked him on Fox News, and on certain things like the Iran nuclear deal and a more confrontational approach towards our allies, Bolton was all in. But on pretty much everything else, they really were substantively very, very different.”

Bolton’s career dates back to the Reagan and George H.W. Bush administrations, but he is perhaps best known for his roles in the George W. Bush administration. As Undersecretary of State for Arms Control and International Security, Bolton was a staunch critic of the U.N. and key supporter of the Iraq War. Bush appointed him U.S. ambassador to the U.N. in 2005 during a congressional recess, after contentious hearings that saw him criticized by Democrats and even some Republicans. He announced his resignation in 2006.

Bolton then became a paid Fox News contributor and senior fellow at the American Enterprise Institute, a conservative think tank where he had previously served as senior vice president.

In June, Trump said on NBC’s “Meet the Press” program that “John Bolton is absolutely a hawk. If it was up to him he’d take on the whole world at one time. But that doesn’t matter because I want both sides.”

Bolton’s clashes with other members of the Trump administration manifested recently in August when, the Washington Post reported, U.S. special envoy Zalmay Khalilzad, who is leading peace negotiations with the Taliban, refused to turn over a draft document of the deal for Bolton to read.

The message sent by this action, according to Hibbard: “Your office leaks.”

“The national security council is the mechanism by which treasury, state, CIA [and the] Department of Defense all kind of exchange information and communicate and coordinate,” he said. “If the head of that is out of the loop, what does that say about the interagency process?

“I think that has a lot to do with Bolton, but it also has to do with Trump and Trump’s style,” he added.

According to James Scott, the Herman Brown Chair and political science professor at Texas Christian University, national security advisers usually perform three roles, two of which Bolton dispensed with: process manager, to ensure a “careful deliberative, interagency process for decision-making”; and honest-broker, to ensure “the information, views and preferences of the main foreign policy advisers are fairly heard and considered.”

The third role is as a policy adviser, offering guidance and recommendations. Scott said that over time, as disagreements between the president and Bolton mounted, he became ineffective at this role as well.

“By this summer he was effectively cut out of the process, with [acting White House Chief of Staff] Mick Mulvaney increasingly usurping his place, and he, the president and Mike Pompeo increasingly antagonistic,” he said. “By this summer, he was not engaged in any of the functions of the national security adviser to any real degree.”

And while world leaders may now be watching the White House to see if Bolton’s exit leads to a shift in America’s foreign policy strategy, the Trump administration is already taking steps to suggest it will be business as usual. At the press conference Bolton would’ve attended if he hadn’t been forced to resign two hours earlier, a smiling Mike Pompeo told members of the press: “I don’t think any leader around the world should make any assumption because some one of us departs, that President Trump’s foreign policy will change in a material way.”

Scott thinks a post-Bolton White House will look much the same as the pre-Bolton one, calling the Trump administration’s foreign policy “shifting and inconsistent.”

And Hibbard questions if there is an articulate foreign policy strategy at all.

“There’s a huge inconsistency between what’s said and what’s done in terms of the Trump administration’s foreign policy, so it’s just not really clear where our foreign policy is going and whether there is any kind of coherent vision,” he said.