By 9 p.m. on Thursday, the spacious West Wing corner office of National Security Advisor Gen. H.R. McMaster sat empty, the door open, the blinds undrawn, pale blue papers on the desk bearing messages from world capitals, unanswered. For White House staffers already on edge after a week of tumultuous personnel and policy change driven by President Donald Trump, the scene represented an ominous calm before the latest, most worrying disruption at the top of American government.

Two hours earlier, Trump had announced on Twitter that he would be replacing McMaster, a temperate, soldier-scholar who had closely hewed to the traditional role of “honest broker” in reconciling the often competing agendas of the CIA, the State Department and the Pentagon, among other foreign and national security agencies in the U.S. government. McMaster would be replaced, Trump tweeted, with the firebrand diplomat and Fox News personality, Amb. John Bolton, a hawkish interventionist with fixed opinions and set agendas.

Bolton will not officially start in the job until April 9, but already moderates in the West Wing are worried. Bolton famously couldn’t win permanent Senate confirmation as Ambassador to the U.N. in 2005, when he was nominated to the position by then-President George W. Bush. He had been criticized by Democrats and some moderate Republicans for intemperance after several witnesses testified to the Senate Foreign Affairs Committee that Bolton had harassed and bullied them. Several floor votes failed to override a Democratic filibuster of his nomination, before he was appointed in recess to the post by Bush.

But more important, he seemed ill-suited for the role of interagency arbiter. “John Bolton does not have a reputation for consensus building within the administration or with allies,” says Michael Green, a senior Asia advisor in Bush’s NSC, now at the Center for Strategic and International Studies. Rather, Green says, Bolton has “a reputation for being an aggressive advocate of his (or in this case the President’s) position. The best national security advisors are usually considered honest brokers, so that would be a different approach from his past M.O., but perhaps one he recognizes is necessary. We’ll have to see”

The record of national security advisors with strong agendas is mixed. Henry Kissinger was successful, though controversial, in the role. Ronald Reagan’s National Security Advisor John Poindexter was convicted of multiple felonies after running a covert operation out of the National Security Council without the knowledge of Congress or other agencies of government. In recent history, Brent Scowcroft is viewed as the most successful holder of the job, thanks to his scrupulous representation to the president of all the views of his national security team, however conflicted.

In previous positions in Republican administrations, Bolton has typically played the role of advocate rather than arbiter. He pushed hard for the invasion of Iraq in 2003, though he argued in favor of leaving the country to rebuild on its own rather than trying to establish democracy there. He is particularly hawkish on Iran and North Korea.

That will make already nervous allies even more uneasy, says Green. “He is a smart, relentless and often effective advocate for his point of view,” Green says, “But he is also seen as more of a bomb thrower than consensus builder and he has advocated the more extreme versions of Trump foreign policy, including military force against North Korea and ending the Iran deal, and this will make allies very nervous. At the U.N., he became more diplomatic and it will be interesting to see how he grows into this role.”

While Bolton’s reputation for stubborn opinions worries some West Wing staffers, any internal disputes it stirs among agencies will fit with the President’s approach to governing. Especially in recent days, the president has preferred disorder and drama over reliability and steadiness. With Bolton in charge of the massive national security decision making apparatus in the White House, Trump may get more drama than he bargained for.

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Write to Philip Elliott at philip.elliott@time.com.