O'Brien also served a member of John Bolton's team during the Bush administration. They worked together at the 60th session of the United Nations General Assembly in 2005.
From 2008 to 2011, O'Brien was appointed to advise the federal government on issues related to the trafficking of antiquities and other cultural artifacts.
During the 2016 presidential election, O' Brien collected a series of foreign policy essays into a book called "While America Slept." He tore into Obama's foreign policy and compared his nuclear deal with Iran to appeasement in Munich that emboldened Adolf Hitler in 1938. "America faces a stark choice in 2016 between a continuation of President Obama’s ‘lead-from-behind’ foreign policy and sequester-based national security approach and a return to President Reagan’s ‘leader of the free world’ foreign policy and ‘peace through strength’ national security approach," O'Brien wrote.
O'Brien praised Trump's national security strategy even before the president-elect was sworn in. In December 2016, he authored a column where he said America's allies were starting to pay more for common defense. "We may be witnessing the most impressive presidential transition from a national-security standpoint in history," he wrote.
In May 2018, Trump picked O'Brien to become his chief hostage negotiator.
Over the summer, Trump sent O'Brien to monitor A$AP Rocky's trial for assault charges after a brawl in Stockholm. “The president asked me to come here and support these American citizens,” Mr. O’Brien told The New York Times. “I’ll be here until they come home.”
O'Brien defended Trump's decision to send him to Sweden, given he usually handles sensitive hostage negotiations in war-torn countries. "The president sent me here, so it’s totally appropriate. I also help free people that are held by governments, so unjustly detained Americans," O'Brien told reporters.
After ousting Bolton as his national security adviser over fundamental foreign policy disagreements, Trump tapped O'Brien to replace him. He made the announcement on Twitter and praised his "very successful" efforts. "I have worked long & hard with Robert. He will do a great job!" Trump tweeted.
Source: President Donald Trump's Twitter account
The national security adviser works directly for the president and is typically tasked with leading the NSC staff that researches military and diplomatic options for the president. The position works with Cabinet level officials like the defense, state and treasury secretaries to present the president with the best policy recommendations.
O'Brien was reportedly boosted by Secretary of State Mike Pompeo, given their work on several hostage cases. They collaborated on the release of Pastor Andrew Brunson in Turkey as well as those of other detained Americans from Afghanistan, Yemen, and Libya.