But whether a smaller, O’Brien-led NSC will have more influence on the president is far from clear. Trump has long chosen his gut instinct over policy advice. And NSC staffers fear the impeachment process, which focuses on whether Trump tried to pressure Ukraine to investigate a political rival, will make the president even less trusting of the U.S. bureaucracy than before.

Several NSC officials have already given damning testimony before House committees, and the whistleblower who first flagged the president’s phone call with Ukraine’s Volodymyr Zelensky is reported to be a CIA employee previously detailed to the NSC staff. President Trump has likened the whistleblower, and the officials who spoke with him, to spies.

For now, O’Brien, who took over in September from ousted conservative hawk John Bolton, appears confident in his approach.

“We're streamlining the National Security Council,” he told CBS News’ “Face the Nation” on Sunday. “We don't need to recreate the Department of Defense, the Department of State, the Department of Homeland Security over at the White House. We've got great diplomats and soldiers and — and folks that can — that do that work for us in the departments.”

POLITICO spoke with several current and former Trump administration officials, as well as outside experts, to get details on the changes. Most requested anonymity because of the sensitivity of the topic, although O’Brien himself has been fairly open about his plans.

The NSC is supposed to act as the body that coordinates U.S. national security and foreign policy across the executive branch. Depending on the administration, its influence has varied.

Trump administration officials say the goal is to reduce the NSC’s policy staff to fewer than 120 people by January. According to O’Brien, the number is coming down from 174. The figure does not count technical and support staff at the institution, which are not expected to see many cuts.

O’Brien has said he’s aiming for a policy staff figure similar to what existed at the NSC during the first term of then-President George W. Bush. Those numbers kept growing — and often exact figures are not revealed — to the point where under President Barack Obama, there were more than 200 policy slots.

The Obama team shrank the body somewhat in its final years, and Trump has continued that.

Much of the shrinkage under O’Brien will be through attrition: Most NSC policy staffers are detailed there from other agencies or departments, such as the Pentagon, typically for a year or two. As their details finish, fewer can expect extensions. Their roles will stay vacant.

The NSC sections slated to lose the most slots are the so-called “functional directorates.” Functional directorates deal with topics unbound by geography, such as human rights or counterterrorism.

At least two functional directorates – strategic planning and emerging technologies – are being phased out, current and former NSC staffers said. The international economics directorate, which previously reported to both the NSC and the National Economic Council, will now report only to the NEC.

An administration official said the strategic planning division had already fulfilled its main mission: crafting Trump’s National Security Strategy. The person who ran that directorate, Kevin Harrington, has been named O’Brien’s strategic counselor, and he’s been tasked with “doing a net assessment of all of our strategies to see how effective our strategies are,” the official said.

Emerging technologies, which in theory tackles topics such as artificial intelligence, was seen as underperforming and duplicative of other parts of the government.

Shifting the international economics directorate is in part about clarifying who’s in charge of what, current and former NSC staffers said. There have been complaints that when the people on that team had a dual reporting structure, in interagency discussions they would play up one or the other depending on what benefited them.

O’Brien also has no plans to revive the Homeland Security Council, which essentially exists only on paper now after initially being a major office under Trump.

The counterparts to the functional directorates are the regional directorates — ones that deal with Europe, the Middle East or South Asia, for instance.

Robert O’Brien (right), who is President Donald Trump’s fourth national security adviser since he took office in 2017, has signaled that he will prioritize regional directorates over functional ones. | Evan Vucci/AP Photo

O’Brien, who is Trump’s fourth national security adviser since he took office in 2017, has signaled that he will prioritize regional directorates over functional ones, a decision that has alarmed some NSC staffers.

One concern is that de-emphasizing functional directorates could lead to different U.S. policies for different regions of the world. And because U.S. officials who deal with regions are highly invested in maintaining relationships with other governments, there’s also a concern they will de-emphasize issues such as human rights or ending corruption.

“The U.S. should, for example, have one approach to democracy and governance globally, not different ones regionally,” one NSC staffer said.

John Gans, author of “White House Warriors,” a book about the NSC and its history, added that other governments may find it disconcerting if in the long run the U.S. doesn’t take the lead on issues that cross national boundaries.

“The transnational stuff — a pandemic, financial crises, climate change — will also still happen but the White House will be less equipped to handle,” he said.

But other observers of the NSC downplayed such concerns, saying that proper communication and coordination can help avoid pitfalls, and stressing that the functional directorates are not being marginalized. Making sure there’s a proper balance, though, will fall to O’Brien and his top deputy, Matt Pottinger, they said.

“I don’t see it as the regional directorates have a greater say — it’s that they must be consulted when they do the work,” a former NSC staffer said.

O’Brien’s decision to promote Pottinger, formerly a senior Asia hand, has been met largely with praise among NSC staffers. O’Brien also has brought over a senior Foreign Service officer, Matthias Mitman, to serve as the NSC’s executive secretary.

Such moves are intentional and differentiate O’Brien from Bolton, who hired several people from outside government to populate the NSC’s top ranks. “If you bring in outsiders, it looks like you’re expressing a lack of confidence in the organization,” the official said.

O’Brien is a lawyer by training, and he first joined the Trump administration as its special envoy for hostage affairs.

O’Brien also has already held several Principals Committee meetings. Such meetings bring together Cabinet members and other top U.S. officials who focus on national security. Bolton was criticized for not holding enough of those gatherings.

Thanks to the impeachment inquiry, the mood at the NSC directorate that deals with Europe and Russia is of special concern to the new NSC leadership. (The current NSC staffer described that directorate as “radioactive.”)

Current and former staffers in that division are among those who’ve had to testify in the impeachment inquiry so far. They include Lt. Col. Alex Vindman, a Ukraine expert is expected to remain at the NSC until July. The senior director for that division, Tim Morrison, recently quit.

He’s been replaced by Andrew Peek, previously a deputy assistant secretary of State for Iraq and Iran. Peek has had relatively little experience dealing with Europe, but he was chosen in part because of his closeness to O’Brien, which should give staffers in that directorate some confidence and comfort.

“He’s a natural leader,” the administration official said of Peek. “He’s going to take care of those guys. The best thing he can do is make sure they’re well represented in the policy process.”

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Like several who filled the role before him, O’Brien has mentioned Brent Scowcroft as a role model for the role of national security adviser.

Scowcroft served in that position under both Presidents Gerald Ford and George H.W. Bush. His model has been described as the “honest broker,” meaning he presented the president with the views of U.S. agencies instead of trying to usurp them with his own.

Aides to Trump, however, concede that although the president likes to solicit a wide range of opinions, ultimately he goes with his own gut. It’s tough to imagine O’Brien changing that, even if he does make the NSC more efficient.

“I think he’s doing the right thing by taking a fresh look at the NSC — what was working and what didn’t,” a second former NSC staffer said of O’Brien. “I think any new national security adviser would do the same thing.”