Trump, who is known to respond well to flattery, has recounted praise from O'Brien in tweets and in conversations, suggesting that the new national security adviser also knows how to handle the President and his mercurial moods.
Robert O'Brien, who has been serving as the special envoy for hostage affairs at the Department of State, has been chosen for the role.
Trump announced O'Brien's nomination on Wednesday, saying that he has "worked long and hard with Robert". "He will do a great job!" the president tweeted from his fundraising trip in California.
Trump recently dispatched O'Brien to Sweden for the court hearing of US rapper A$AP Rocky, who was later convicted for assault.
"O'Brien joined the administration in May 2018 and serves as the Special Presidential Envoy for Hostage Affairs at the State Department. Pompeo may not be dual-hatted as secretary of state and NSA, but he might as well be with this arrangement", a former national security council spokesman, Ned Price, said on Twitter.
U.S. policy of ‘maximum pressure’ will fail, Iran’s Supreme Leader vows
President Trump is "obligated to try and find peace", he said. "I'm somebody that would like not to have war", he said. Iran's Foreign Ministry spokesman Abbas Mousavi dismissed Washington's accusations, calling them "blind and futile".
O'Brien has helped free USA hostages including Danny Burch, an engineer at an oil company who was taken hostage by a criminal gang in Yemen. It will be interesting to see how O'Brien works under Trump.
He worked with Bolton at the United Nations under President George W. Bush, who appointed him in 2005. O' Brien was confirmed by the Senate.
In a 2016 book on the United States' role in the world entitled While America Slept, O'Brien is very critical of former US President Barack Obama's foreign policy. His instincts for an aggressive, interventionist foreign policy were at odds with Mr Trump's more isolationist stance.
He also was an adviser on the Republican presidential campaigns in the past of Ted Cruz, Mitt Romney and Scott Walker. O'Brien also coordinates with the interagency Hostage Recovery Fusion Cell on the development and implementation of US hostage recovery policy and strategy.
He has also been the only US official consistently working on releasing Americans imprisoned in Iran. Trump said last week that he'd asked his chief diplomat if he was interested in also taking on the national security adviser job but that he had declined.