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 political advice. And NSC employees fear the impeachment process, which focuses on whether Trump tried to pressure Ukraine to investigate a political rival, will make the president even less confident of the US bureaucracy than before.
Several NSC officials have already provided condemning testimony to the House committees, and the whistleblower who first flagged the President's telephone conversation with Ukraine's Volodymyr Zelensky is reported to be a CIA employee previously described to NSC staff. President Trump has been similar to the whistle and the officials who spoke to him as spies.
At the moment, O'Brien, who took over in September from the removed conservative hawk John Bolton, seems confident in his attitude.
"We streamline the National Security Council," he told CBS News "Face the Nation" on Sunday. “We do not need to recreate the Ministry of Defense, the Ministry of Foreign Affairs, the Department of Home Security at the White House. We have amazing diplomats and soldiers and ̵
POLITICO spoke with several current and former Trump administration officials, as well as external experts, to get information about the changes. Most people requested anonymity because of the sensitivity of the subject, although O'Brien himself has been fairly open about his plans.
NSC is intended to act as the body that coordinates US national security and foreign policy throughout the executive branch. Depending on the administration, its influence has varied.
Trump administration officials say the goal is to reduce NSC's policy staff to fewer than 120 people in January. According to O'Brien, the number will fall from 174. The figure does not include technical and support staff at the department, who are not expected to see many cuts.
O'Brien has said that he is aiming for a staff of personnel similar to what was at NSC during the first term of then-President George W. Bush. These numbers continued to grow – and often not exact numbers are revealed – to the point where there were more than 200 political gaps under President Barack Obama.
The Obama team has shrunk slightly in the last few years, and Trump has continued to do so.
Much of the shrinking under O'Brien will be through exhaustion: Most of the employees in NSC policy are detailed there from other agencies or departments, such as the Pentagon, usually for a year or two. When their details end, fewer can expect extensions. Their roles remain vacant.
The NSC sections for losing most places are the so-called "functional directorates." Functional directorates deal with topics that are not bound by geography, such as human rights or terrorism.
At least two functional directorates – strategic planning and new technology – are being phased out, said current and former NSC staff. The International Finance Directorate, which previously reported to both the NSC and the National Economic Council, will now only report to the NEC.
An administrative official said that the strategic planning department had already fulfilled its main mission: designing Trump's national security strategy. The person who led this directorate, Kevin Harrington, has been named O'Brien's strategic advisor, and he has been commissioned to "do a net appraisal of all of our strategies to see how effective our strategies are," the official said.
Growth techniques, which in theory deal with subjects like artificial intelligence, were seen as underperforming and duplicated by other parts of the government.
Moving the International Finance Directorate is partly about clarifying who is responsible for what, said current and former NSC staff. There have been complaints that when the people in that team had a dual reporting structure, in interagency discussions they would play one or the other depending on what favored them.
Nor does O'Brien have any plans to revive the Homeland Security Council, which essentially only exists in paper now after being headquartered under Trump.
The counterparties to the functional directorates are the regional directorates – those, for example, dealing with Europe, the Middle East or South Asia.