VOA National Security Correspondent Jeff Seldin contributed to this report.

President Donald Trump has named hawkish diplomat Robert O’Brien as his new national security adviser, replacing another foreign policy hawk, 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! — Donald J. Trump (@realDonaldTrump) September 18, 2019

In his State Department position, which he held from May 2018, O’Brien worked closely with families of American hostages and advised the Trump administration on hostage issues. He previously helped lead the agency’s initiative for justice reform in Afghanistan during the administrations of Presidents George W. Bush and Barack Obama.

Hawkish views

O’Brien outlined his hawkish world views in a 2016 book, “While America Slept,” in which he criticized Obama as weak on foreign policy, particularly for joining a 2015 deal in which world powers offered Iran sanctions relief in return for restraining its nuclear program.

O’Brien called it “the worst diplomatic deal since Munich,” a reference to a 1938 agreement in which European powers acquiesced to Nazi Germany’s annexation of the Sudetenland region of then-Czechoslovakia.

In the book, O’Brien also referred to Iran as a “sworn enemy” of the United States.

“It’s a privilege to serve with the president,” O’Brien said to reporters as he stood alongside Trump, who was on a campaign fundraising trip to California.

This image provided Sept. 15, 2019, by the U.S. government and DigitalGlobe and annotated by the source, shows damage to the infrastructure at Saudi Aramco's Kuirais oil field in Buqyaq, Saudi Arabia.

Challenges in Middle East

O’Brien’s appointment comes as Trump is confronted with multiple challenges in the Middle and Near East, including how to respond to weekend attacks on oil facilities in Saudi Arabia, a U.S. ally, and how to negotiate peace agreements in Afghanistan’s civil war and between Israelis and Palestinians.

The Trump administration also faces what it sees as increasing regional aggression from Iran, the target of new sanctions Trump announced just moments before tweeting about O’Brien’s appointment.

“Any advice I give the president would be something I give him confidentially,” O’Brien said in response to a reporter’s question about Iran and Saudi Arabia.

Trump said Bolton had been a “disaster” on North Korea policy, “out of line” on Venezuela, and did not get along with important administration officials.

“The new national security adviser is starting off with what John Bolton apparently always lacked: a good working relationship with the U.S. president,” said Franz-Stefan Gady, senior fellow at the EastWest Institute, a U.S. nonprofit group focused on international conflict resolution. In a message to VOA Persian, Gady said O’Brien “would do well not to give in to any hawkish tendencies, as the U.S. president has repeatedly signaled that he is not willing to go to war in the Persian Gulf.”

O’Brien, Trump’s fourth national security adviser, was chosen from a list of five candidates.

Lacks depth of experience

Larry Pfeiffer, director of the Michael V. Hayden Center for Intelligence, Policy and International Security at George Mason University, told VOA he does not know O’Brien but notes “(O’Brien) 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 advisers is telling,” Pfeiffer added.

Robert O'Brien sent a letter to ⁦@JZarif⁩ back in April with regards to the fate of US prisoners in Iran. While quite a hawk, he seems more open to engaging the Iranian govt than his predecessor. https://t.co/JfVDThDBUz — Ali Vaez (@AliVaez) September 18, 2019

Ali Vaez, an Iran analyst at the Belgium-based International Crisis Group that also seeks to prevent wars, tweeted that while O’Brien is “quite a hawk, he seems more open to engaging the Iranian (government) than his predecessor.”

In a message to VOA Persian, Vaez said he learned from senior Iranian officials in New York that O’Brien wrote to Iranian Foreign Minister Mohammad Javad Zarif in April, regarding the fate of Americans held in Iran.

Envoy for hostage affairs

In O’Brien’s previous role as a U.S. envoy for hostage affairs, he communicated with families of those Americans, including the family of Robert Levinson, who went missing in Iran 12 years ago and whose relatives believe Iran detained him.

FILE - Undated handout photo shows retired FBI agent Robert Levinson. His family received this photograph in April 2011.

The retired FBI employee was working as a private investigator when he disappeared March 9, 2007, while visiting Iran’s Kish Island. Iranian officials have denied knowledge of his whereabouts.

“Our family is very glad to hear of Robert O’Brien’s appointment,” the Levinson family said in a statement sent to VOA Persian. “This is further evidence of President Trump’s commitment to bringing home Americans held abroad. We look forward to continuing to work with Ambassador O’Brien and the National Security Council to bring Bob Levinson home to those who love him.”

Rapper’s case in Sweden

Trump also 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 commentators who believed Trump had inappropriately intervened in the legal affairs of an allied nation.

In 2005, 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 Gov. Scott Walker, former Massachusetts Gov. Mitt Romney and Sen. Ted Cruz of Texas.

O’Brien was a major in the U.S. Army Reserve. After graduating from the University of California-Berkeley School of Law, he founded a law firm in California that focused on international arbitration issues.

As national security adviser, O’Brien will be the highest-ranking Mormon in the U.S. government, a notable development for a 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.