WASHINGTON (NYTIMES) - Even his many critics conceded that former national security adviser John Bolton brought useful credentials to the job: decades of foreign policy experience and a keen grasp of how the gears of government turn.

Mr Bolton's main problem, as it turned out, was that he knew too much. Confident in his experience to a fault, he was unwilling to shade his deeply held hawkish views, which he defended with a prickly personality that alienated colleagues - and ultimately President Donald Trump, leading to his ouster last week.

Mr Robert O'Brien, Mr Trump's choice to succeed Mr Bolton, flips that equation.

He is a former Los Angeles lawyer with limited government experience before he became the State Department's point man for hostage negotiations.

But his friends all cite an affable, ingratiating personality that has earned him allies throughout the Trump administration.

Mr O'Brien has a record of traditional conservative foreign policy views and has supported a tougher approach toward China, Iran and Russia. And Mr O'Brien served with Mr Bolton when he was President George W. Bush's ambassador to the United Nations.

Friends and Trump officials say that while Mr Bolton saw himself as a crusader for specific policy goals - and some said a necessary counterweight to Mr Trump's instincts - Mr O'Brien, 53, is more likely to act as an arbiter of competing views and a facilitator of Mr Trump's decisions.

One Trump official said that Mr O'Brien would bring "no outside agenda" to the job.

But questions remain about whether Mr O'Brien's background has adequately prepared him for the myriad challenges of his new job.

Mr Trump is currently navigating, among other things, a broiling crisis with Iran, a deadlocked trade war with China, a stalemate in nuclear talks with North Korea and the recent collapse of peace talks in Afghanistan.

Mr O'Brien will be Mr Trump's fourth national security adviser in three years, the most any president has had in a first term.

Speaking to reporters in Los Angeles on Wednesday with Mr O'Brien by his side, Mr Trump suggested they were off to a good start.

"I think we have a very good chemistry together, and I think we're going to have a great relationship," Mr Trump said. "He is a very talented man."

In brief remarks, Mr O'Brien twice mentioned the goal of maintaining "peace through strength", perhaps best known as a catchphrase of former President Ronald Reagan.