It has been about four days since President Donald Trump appointed former U.S. ambassador John Bolton to be his next national security adviser, and the reactions have ranged all over the map. Fellow uber-hawks like Senators Lindsey Graham and Tom Cotton are charged up about Bolton joining Trump’s national security team, while the rest of us are heading to church and praying that the rapture won’t come early. For those in the a realist persuasion who prize diplomacy as a preeminent foreign policy tool rather than a form of appeasement, it’s hard to find anyone who would be as terrifying in the Situation Room as Bolton. What’s next? Another stint for Dick Cheney as secretary of defense?

As dangerous as Bolton’s foreign policy views are—which, if one were to sum them up, consist of bombing any adversary callous enough not to succumb to America’s wishes—his cutthroat, take-no-prisoners approach to policymaking should be just as nerve-wracking. With experience across three administrations, Bolton’s bureaucratic chops are as ruthless as his mustache is bushy. He takes the national security bureaucracy by the horns and is not afraid to play dirty.

During his previous tenures in government, Bolton was not at all concerned with smashing heads. He wasn’t there to make friends, but to advocate for his hardline principles and marginalize those who were too weak, squishy, or stupid to agree with his wisdom. If he found himself running up against a wall of resistance, he pushed harder until all his governing muscles atrophied. Bolton’s colleagues in the George W. Bush administration have detailed horror stories, describing a man who is irascible, difficult to work with, and churlish when he doesn’t get his way.

Emails disclosed by the New York Times in 2005 show Bolton and his top staffer battling with career intelligence officers over specific wording in a speech he was prepared to deliver at a think tank. When the intelligence community refused to clear Bolton’s comments about Cuba developing a biological weapons program, Bolton had a fit, summoning the analyst responsible to his office and screaming at him for being insubordinate. And when the analyst refused to be intimidated by his antics, Bolton appealed to the official’s superiors to get him removed. The play didn’t work, but it demonstrates the extent to which Bolton retaliates when challenged.

Another 2005 article in the Washington Post reported that Bolton would block Iran-related memos from Secretary of State Colin Powell and National Security Advisor Condoleezza Rice, which contributed to dysfunction at a time when the Bush White House was deliberating about whether to take the Iran nuclear issue to the U.N. Security Council. Just the other day, a former Israeli ambassador recollected his time working with Bolton at the U.N. Bolton, the ambassador said, would often warn him when a Security Council resolution he believed was anti-Israel was close to be filed for a vote. That would all be well and good, but those same resolutions were actually drafted by the U.S. with the support of Condoleezza Rice, Bolton’s boss at the time. If true, what the ambassador alleges is insubordination—yet another case of Bolton doing everything in his power to scuttle an initiative he vehemently opposed.

Bolton is reportedly cognizant of all of this. He knows that many security officers in the cabinet don’t trust him to run a neutral policy process where the recommendations and concerns of all agencies and departments are given equal consideration. But old habits die hard. When you’ve spent a lifetime in the bureaucratic trenches lobbing grenades at anyone and everyone who opposes your efforts, it can be difficult to cease fire, climb out of the foxhole, and try to reach peace with your enemies.

This is, of course, precisely what John Bolton needs to do. The national security advisor is one of the most important positions in the U.S. government, and those who have held the job in the past will tell you that it requires wearing a number of hats: chief implementor and enforcer of the president’s agenda; mediator between the Pentagon, the State Department, and the White House staff; special envoy on the National Security Council, where establishing a consensus is paramount; and trusted confidant of the president, who needs to feel at ease when making critical life-and-death decisions. H.R. McMaster apparently never had the trust aspect, nor was he able to hold people in the inter-agency accountable when options were deliberately stalled or ignored. With decades of experience across three administrations, perhaps Bolton will be considerably more equipped to handle it.

The ambassador’s biggest task, however, is to keep an open mind and check his temper at the West Wing’s main gate. Bolton cannot afford to return to his worst impulses, whether it’s losing his cool, berating his colleagues, or threatening to fire someone for presenting an alternative intelligence assessment. Bolton will make his views known—as he should, even if those views would make the warriors of Ancient Sparta blush—but he should not browbeat the inter-agency process to accept them. The president and the country would not be served if his old trucks return.

With so many crises on his plate, President Trump must be presented with all credible national security options regardless of whether John Bolton agrees with them or not. If Bolton can perform that responsibility, more power to him. But if he doesn’t live up to the job, it is the country that will suffer.

Daniel R. DePetris is a foreign policy analyst, a columnist at Reuters, and a frequent contributor to The American Conservative.