President Donald Trump has named Robert O'Brien as his new National Security Adviser, replacing John Bolton who was fired last week.
"I am pleased to announce that I will name Robert C. O'Brien, currently serving as the very successful Special Presidential Envoy for Hostage Affairs at the State Department, as our new National Security Advisor. I have worked long & hard with Robert. He will do a great job!," Trump said on Twitter Wednesday.
Trump had said Bolton had been a "disaster" on North Korea policy, "out of line" on Venezuela, and did not get along with important administration officials.
O'Brien, Trump's fourth national security advisor, was chosen from a list of five candidates Trump said were under consideration.
He was selected after having collaborated with Secretary of State Mike Pompeo on a number of hostage situations.
In his State Department position, which he held since May 2018, O'Brien worked closely with families of American hostages and advised the administration on hostage issues. He previously helped lead the agency's initiative for justice reform in Afghanistan during the administrations of George W. Bush and Barack Obama.
Trump sent O'Brien to Sweden earlier this year to monitor the criminal case against American recording artist A$AP Rocky, who was found guilty of assault in August. O'Brien's presence in Stockholm drew criticism from critics who believed Trump had inappropriately intervened in the legal affairs of an allied nation.
In 2005, President Bush nominated O'Brien to be U.S. Representative to the U.N. General Assembly, where he worked with Bolton. At the time Bolton was U.S. Ambassador to the United Nations.
O'Brien has also served as an adviser to the Republican presidential campaigns of former Wisconsin Governor Scott Walker, former Massachusetts Governor Mitt Romney and Senator Ted Cruz of Texas.
O'Brien was a major in the U.S. Army Reserve and, after graduating from the University of California-Berkeley School of Law, founded a law firm in California that focused on international arbitration issues.
Larry Pfeiffer is a former CIA chief of staff and former senior director of the White House Situation Room who is now director of the Michael V. Hayden Center for Intelligence, Policy and International Security at George Mason University in Virginia.
Pfeiffer told VOA he does not know O'Brien but notes "he doesn't have the depth of national security experience of any of his recent predecessors."
"He seems to be a thoughtful man who loves his country, but who likely just took the first step towards an early return to his successful law practice, if the president's history with national security advisors is telling," Pfeiffer added.
As national security advisor, O'Brien will be the highest-ranking Mormon in the U.S. government, a notable development for church that has shown some wariness of Trump. The religious community is also expected to be a significant voting demographic in certain states in the 2020 presidential election.
O'Brien's appointment comes as Trump is confronted with multiple crisis in the Middle East, including efforts to help negotiate peace agreements in Afghanistan and the Taliban and between the Israelis and Palestinians.
The administration is also struggling with how to deal with an increasingly aggressive Iranian regime, the target of new sanctions Trump announced just moments before tweeting he had named O'Brien for his new position.
VOA National Security Correspondent contributed to this report