On a more prosaic level, however, there is the fear that Bolton will succeed in navigating the Swamp where so many other Trump advisers have failed. “Everyone that knows him knows that he is very smart, and not only is he very smart, but he is very effective,” a former senior U.S. official cautioned. “Bolton is so dangerous because he is good at what he does.” Ian Bremmer, a foreign-policy analyst and founder of the Eurasia Group, described Bolton as “extremely bureaucratically capable”—an infighter with sharp elbows and a tactile understanding of the media. “He knows how to get in meetings that matter, he knows how to play the media, and he is going to push hard to be a very strong national security adviser with those views vis-à-vis his colleagues in Cabinet.”

While Pompeo has ingratiated himself, for example, by telling Trump what he wants to hear, critics worry that Bolton will push the president further, tapping into his most aggressive instincts at a moment when the United States is facing a foreign-policy minefield. “To be honest, I think the president is more pragmatic,” a former State Department official, who knows Bolton, told me. “[Trump’s] business background seems to lean him more toward looking for a deal, not being wedded to a sharp position.” As the president’s top adviser on national security, however, Bolton will be rivaled only by Chief of Staff John Kelly and Defense Secretary James Mattis for power in the West Wing. “We know that Trump is clearly influenced by some of the last people that he speaks to,” the Senate aide added. “Besides the chief of staff, the national security adviser is usually the last person that speaks to the president before a major decision.”