Erin Scott / Reuters

John Bolton’s sudden departure from the Trump administration was inevitable. It had nothing to do with his fabled mustache or even his very real personality clash with the president. It was a matter of principle. Trump wants to write a new chapter, closing the one marked “Militarism and Maximum Pressure” and opening one called “Dealmaking and the Pursuit of the Nobel Peace Prize.” He wants a summit with Iran’s leaders and deals with the Taliban, Kim Jong Un, and Vladimir Putin on arms control. He does not care about most of the details, as long as he gets the credit.

Few of his officials are particularly enthusiastic about this pivot, but led by Secretary of State Mike Pompeo, they accept it and will seek to shape it. Bolton did not accept it—with the exception of Russia, where he was playing a constructive role in advancing Trump’s goals—and played the role of a saboteur. This tension has been clear for several months, but with Bolton keen to hang on and Trump famously averse to personal confrontation, it dragged on over the summer. With a Trump summit with Iranian President Hassan Rouhani now imminent, it could not drag on much longer. And earlier this week, it came to an end.

I talked with several current or former Trump-administration officials for this piece, all of whom spoke under condition of anonymity to freely discuss Trump’s foreign policy after Bolton. These officials had different views of Bolton. Some saw him as brilliant and a surprisingly good diplomat who fell down on issues such as Iran, Cuba, and Venezuela, where he took a particularly hard line. Others were less forgiving, and argued that Bolton had failed to work well with other senior officials to advance Trump’s strategy.

But all agreed that the Trump pivot is real. We are entering into a new phase. Trump has always had two images of himself on national-security issues—as a militarist and as a dealmaker. As he nears the election, he hopes to move from the former to the latter, spending the capital he built up as a hard-liner, and wrong-footing his Democratic opponents. Ever since he got rid of the axis of adults, he has sought to remove the institutional constraints on his decision making, allowing him maximum room to maneuver in line with his instincts and core beliefs, which date back more than three decades.

If Bolton does speak out, it will grow harder for the so-called hawks in Congress to turn a blind eye to criticism from centrists, and to continue to support Trump unconditionally. This is particularly true given that Bolton’s critique of Trump concerns Iran, an issue about which they care passionately. It is not far-fetched to imagine Trump meeting Rouhani with Bolton criticizing the summit live on cable news. Trump will likely react as is his wont—with full-scale attacks on Bolton personally, and on anyone who associates with him. The result could be a new Republican divide on foreign policy, with the challenge coming from the right.

Trump, of course, will have his supporters on the subject. As one official told me: “Trump is right in his orientation. We need to focus first on China. So, ultimately, we do need to get to a different place with the Russians. The more distracted we are by North Korea, the better for Beijing. And we need to get out of Afghanistan or really reduce our role there.” But many Republican foreign-policy experts remain unconvinced.

The international repercussions of this diplomatic pivot will be profound, particularly because it will be carried out with Trumpian characteristics—with little formal preparation, a focus on summits, and an eye on the politics. Martin Indyk, who served in several senior positions in the Clinton and Obama administrations, posed some interesting questions on Twitter: “What do Kim, Rouhani, Xi and the Taliban conclude about Trump’s need for deals with them? And what do Bibi and MBS do as the limb they’re on gets sawn off?” he asked, referring to the Israeli and Saudi leaders. These are the right questions to ask. Absent an external crisis, Trump’s diplomatic pivot will define world politics for the next year, and it has a dynamic of its own. In particular, it puts America’s rivals in pole position. They know that Trump needs his talks not to fail, and they hope he will make concessions to keep them afloat.

Jung Pak, my colleague at the Brookings Institution and formerly an analyst at the CIA, told me, “Kim Jong Un perceives he is in a position of strength going into 2020, and the closer we get to the election, the weaker Trump will be and the more he will want to deal. Trump is so invested in a win with North Korea that all Kim has to do is whisper quietly that he is thinking about breaking the Singapore promises to secure concessions from the United States.”

Iran may be in an even stronger position. It could allow the talks to gather pace and then weaponize its diplomacy with Trump as the election approaches. Russia is in a slightly different category, because Putin likely wants Trump to win reelection. Putin could capitalize on an arms-control agreement to smooth his reentry into the G8 and have some sanctions lifted.

Meanwhile, Israeli Prime Minister Benjamin Netanyahu and Saudi Arabia’s Crown Prince Mohammed bin Salman will be left to stew in their own juices. They only have themselves to blame. They cheered Trump leaving the Iran nuclear deal, but erred in believing they could control the fallout. Trump did what they wanted at the beginning, but he was always unlikely to use force, making diplomacy a more likely outcome.

Trump’s most immediate challenge is picking Bolton’s replacement. More than a dozen names are floating around Washington. If he is true to past form, Trump will revel in the drama and have a parade of candidates interview with him. However, he ultimately has a choice to make—does he go with a personal advocate who will fight for him, or does he go with a seasoned professional?

He may be tempted to go with an advocate like Richard Grenell, the U.S. ambassador to Germany. Grenell is often regarded as a Bolton ally because he served as his spokesman when Bolton was ambassador to the United Nations. But Bolton and Grenell have not been on particularly good terms for the past 18 months. Grenell has been gunning for Bolton’s job from the beginning, frequently using his connections to Trump’s family, particularly Donald Jr., to advance his case. Those ties were in evidence in a tweet by the president’s son in March, when he called for the U.S. ambassador to Ukraine to be fired. He wrote: “We need more @richardgrenell’s and less of these jokers as ambassadors.” Grenell is in Washington this week, having arrived extra early for the UN General Assembly, and will have dinner with Trump on Saturday night—several observers I spoke with believe he is actively angling for the job. Donald Jr.’s support and Grenell’s own tensions with Bolton may work in his favor, but he has other problems.

Trump has no time for bureaucracy or process, but he is tired of the infighting among his staff. He does not care much for the interagency process, but he does understand that if he is to succeed in his pivot, he needs his team to meet a minimum level of cooperation. Grenell would make the combative Anthony Scaramucci look like Mahatma Gandhi. He clashed repeatedly with other administration officials and with other U.S. ambassadors in Europe. Many National Security Council staffers have made clear they would leave if he was appointed. And Grenell has a strained relationship with Pompeo, including a very public disagreement about whether he could fly the rainbow flag over the U.S. embassy in Germany on Pride Day. Under Grenell, an implosion of what’s left of the National Security Council process seems likely. Ultimately, it is hard to imagine Trump staking the success of his pivot on Grenell.

If he passes on Grenell but still wants an advocate, he could opt for retired Colonel Douglas Macgregor, who regularly appears on Tucker Carlson’s show on Fox News. Macgregor always strikes a Trumpian tone and has endorsed the president’s views on Syria and Russia. Trump has consulted with Macgregor on national-security matters, including when he canceled the planned missile strikes on Iran in June. However, Macgregor poses one of the same problems as Grenell—he may not actually be able to deliver the diplomatic pivot and he would be seen as a disastrous appointee by the Republican foreign-policy establishment.

If Trump decides to go for a serious professional who follows his lead and works well with Pompeo, he has several options. The top two may be Steve Biegun, the president’s special envoy for North Korea, and Rob Blair, who serves as Mick Mulvaney’s national security adviser. Both are well regarded by their colleagues, but have less of a relationship with Trump. Robert O’Brien, who currently serves as the U.S. special envoy for hostage affairs, is said to have the backing of Republican House Minority Leader Kevin McCarthy and several other influential figures.

Brian Hook, the U.S. envoy for Iran, has also been mentioned, and is close to Pompeo. He is well regarded by Republicans, although some worry that his focus on Iran and the Middle East may detract from Asia and Europe. He could also enter the frame if Pompeo were to follow the lead of Henry Kissinger, and take on the dual role of secretary of state and national security adviser. Pompeo will be wary of this option. He has the Goldilocks level of access to Trump at the moment—enough to always matter, but not so much that he gets under Trump’s skin. But if he fears the wrong person being tapped for the job, he may try to take it on himself, delegating much of the day-to-day responsibility to a deputy like Hook.

Regardless of whom he chooses, Trump is in control. He is calling the shots. Those who survive, like Pompeo, do so because they accept this. Newcomers like Mark Esper are learning the same lesson—he recently raided funds assigned for the U.S. military to counter Russia in Europe to pay for the wall on the southern border. The next national security adviser will have to make similar compromises with his own principles.

Many people will undoubtedly breathe a sigh of relief that Trump is embracing diplomacy, but with Trump, things are never that simple or straightforward. His focus on the political benefits of negotiation and his egomaniacal desire to be seen as a dealmaker extraordinaire could undo his project, bringing about the very crises he hopes to avoid.

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