After his election in 2016, Mr. Trump took a tour of the White House and was reportedly “awed” at the size and scope of the issues that came to the president’s desk and the system that delivered them there. It is no surprise why: Mr. Trump had never served in the military or government of any kind. Managing it all got more daunting when his first national security adviser, Michael Flynn, resigned in disgrace, and the president did not get along with his eventual replacement, H.R. McMaster.

Although denied high-level positions early in the Trump administration, Mr. Bolton, who replaced General McMaster in April 2018, could have been a good fit for the job under an inexperienced president. Compared with Mr. Flynn and General McMaster, Mr. Bolton is a seasoned Washington player, one who considers himself a “good bureaucrat.” Even if he never shared all Mr. Trump’s policy preferences, Mr. Bolton was well positioned to work the levers of government for him.

Instead, Mr. Bolton decided to break the interagency system that had served as the heart of American foreign policy for over seven decades. Driven by confidence in his own ideas about what government should do and how it should run, he had in mind something closer to Roosevelt’s juggling: The president in a room with the national security adviser and a few aides making decisions about most important issues in the world. To realize that plan, Mr. Bolton included fewer people in meetings, made council sessions far less regular, and raced to always be by Mr. Trump’s side. There was no longer a National Security Council, in effect, just a national security adviser.

Mr. Bolton broke government and then it broke him. As the national security adviser, he pushed for a hard line on North Korea, Iran, Venezuela and Afghanistan. But without a structure behind him, Mr. Bolton was increasingly alone trying to sell positions that were a hard sell to Mr. Trump, who is much less an ideologue and much harder to pin down. Eventually, Mr. Trump split with Mr. Bolton and began consulting with outsiders like the Fox News personality Tucker Carlson. When Mr. Bolton fell out with the president, the ad hoc system collapsed right along with him, as reports over the messy decision-making on the proposed Afghanistan peace deal and talks demonstrate.

Mr. Bolton’s singular achievement was to dismantle a foreign-policymaking structure that had until then kept the president from running foreign policy by the seat of his pants. Mr. Bolton persuaded Mr. Trump he didn’t need the National Security Council to make decisions; it is no surprise that the president eventually felt confident deciding he did not need a national security adviser, either. Whether Mr. Trump names a replacement for Mr. Bolton does not matter: No one is going to convince the president he needs a system now, let alone the one that existed for 70 years.