Bolton
National Security Advisor and distinguished maniacJohn Bolton
Bolton let's Trump have all the spotlight, flatters him, plays the loyal servant, but meanwhile he's carefully isolating him from all non-Bolton people and opinions

Curt Mills reports on Bolton's extensive and expanding influence in the Trump administration:
But in the meantime, in return for his occasional, minor humiliation, Bolton enjoys wide-ranging authority to craft the national security policy of the United States, behind the scenes. He's the contra Mattis; instead of resigning in moral protest, Bolton wears the mask of obsequiousness, while subtly nudging a reluctant president toward a more tough-minded line.
We have seen how Bolton has been able to delay and even partially undo one of the president's initial decisions in Syria (all the while emphasizing that the president's decision was being faithfully carried out), and his fingerprints are all over the demise of the INF Treaty. Now we are starting to see the same thing happen with North Korea policy.

Bolton's combination of shameless flattery of the president and relentless promotion of hard-line policies threaten to usher in one or more foreign policy debacles in the remaining years of the Trump presidency.

The National Security Advisor is horrible at his official job of organizing and running a competent policy process, but he has been able to exploit the ensuing dysfunction to advance his own agenda. He will rarely contradict Trump in public, and even when he does he will deny that he is doing it, and that affords him the luxury of being to craft his own foreign policy with as little input from the rest of the administration as possible.

The predictable result is an increasingly confrontational and reckless set of policies. Because he doesn't advertise his influence and consistently minimizes his role in public statements, he avoids wounding Trump's vanity and secures his ability to lead Trump where he wants him to go. Judging from Bolton's record, that means new wars and explicit policies of regime change.

Likewise, there was an important detail in this article on Bolton and the National Security Council that merits a few comments:
But before he resigned, the defense secretary wrote a sharply worded letter to Bolton, insisting that the paucity of meetings was crippling the policy process. Mattis was particularly upset that not a single principals committee meeting had been held to discuss U.S. withdrawal from the Intermediate-Range Nuclear Forces Treaty with Russia, the INF[bold mine-DL].
There have not been many of these meetings since Bolton took over as National Security Advisor, and this has been most noticeable for some of the most important decisions that Trump has taken as president. There weren't any meetings held to discuss abandoning the Joint Comprehensive Plan of Action, and there weren't any held to discuss quitting the INF Treaty. Major administration foreign policy decisions have been made without serious consideration of their costs and potential pitfalls, and that's because Bolton doesn't want those costs and pitfalls to be considered.

Anthony Blinken wrote about this earlier this year, and he explained that the lack of these meetings increases Bolton's control over policy:
Under Mr. Bolton, the National Security Council headed by the president, the Principals' Committee headed by Mr. Bolton and the Deputies Committee, which I once led and which coordinates policy deliberations, have gone into deep hibernation.

Some combination of these committees typically met multiple times a day. Now, it is reportedly once or twice a week at most.

The result is greater control of the policy process for Mr. Bolton and fewer messy meetings in which someone might challenge his wisdom. Mr. Mattis, who once complained about death by meetings, protested to Mr. Bolton about the lack of them.
Bolton has no interest in hearing dissenting views, and he certainly doesn't want to present those views to the president. He does a truly terrible job of running a policy process that presents the president with a full range of views and options because he long ago decided what the policy should be. Bolton hated both the INF Treaty and the JCPOA, and he was determined to get the U.S. out of both. Why would he bother consulting with other members of the administration when they might have a different opinion?

The result is that an ideologue answerable to no one but the president has acquired unusually great influence over the substance of major foreign policy decisions, and all the while he keeps up the pretense that he is merely an adviser.