He seduced the president into the job by releasing a number of Americans imprisoned by foreign governments and armed groups. Mr Trump sees the release of detained Americans as a strategic “victory” that even his critics are reluctant to question, and Mr O’Brien is continuing these lawsuits in his new job.
Some White House colleagues have joked that navigating a situation filled with his experience is the ideal preparation for serving Mr. Trump. The president, on his behalf, praised Mr O’Brien’s good behavior and praised Mr O’Brien’s fair behavior and useful cases after he alleged that Mr McMaster and Mr Bolton’s outrageous personalities and his swaggering jokes were often personal.
Mr. O’Brien became better than his predecessors with Mr. Pompeo, who disagreed with Mr. Bolton, and with Mr. Trump’s son-in-law, Jared Kushner, who often gave foreign policy advice. For more than a decade he has been friends with Mr. Grenell, the latest addition to the National Security Force.
He talks to the president several times a day, often in the early morning and sometimes in the private residence of the White House before Mr. Trump arrives at the Oval Office.
But he has nothing to do with Mr. Trump or the previously known affection for the president’s “America First” nationalism style. He authored an article published in 2016, channeling mainstream conservative views.
Some national security professionals who have worked with or advised Mr O’Brien said he was wrong to be underestimated and had a skilled management touch that replaced his work with dozens of lawyers in the Los Angeles office of Arant Fox, a Washington law firm.
Others complain that he lacks credibility on policy details, and that his chief deputies are Matthew Pottinger, a former Wall Street Journal reporter and a Marine who has been in a handful of White House support for Mr. Trump’s three-year presidency.
In a television interview in late December, Mr O’Brien mistakenly referred to the North Korean ruler, Kim Jong-un, to change the leader’s name for the one he had given. It was, his critics said, not the mistake that an experienced officer made.
Julian E. Barnes, Adam Goldman, Katie Rogers and Edward Wong contributed to the report.