Hostage negotiator Robert O’Brien, who has a history in Republican foreign policy circles, will replace John Bolton.

US President Donald Trump on Wednesday named hostage negotiator Robert O’Brien as the new White House national security adviser.

O’Brien, who currently serves as the special presidential envoy for hostage affairs at the State Department, has a long history in Republican foreign policy circles.

He will be Trump’s fourth national security adviser, replacing John Bolton, the hawkish national security adviser the president forced out last week. Trump said he and Bolton “strongly disagreed” on a number of issues including North Korea and Venezuela.

“I have worked long and hard with Robert,” Trump tweeted in his announcement of the replacement. “He will do a great job!”

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

Trump’s announcement comes as the US considers its response to Saturday’s attacks on Saudi Arabian oil facilities.

It also comes less than a month after Trump abruptly ended talks with the Taliban aimed at starting the process of ending 18 years of war in Afghanistan.

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O’Brien is a lawyer from Los Angeles who has served as a foreign policy adviser to several Republican presidential campaigns, handled a number of prominent legal cases and previously served in several State Department positions.

From 2008 through 2011, O’Brien was a presidentially appointed member of a government committee that advises on issues related to the trafficking of antiquities and other cultural items. In 2005, President George W Bush nominated O’Brien to be US Representative to the UN General Assembly, where he worked with Bolton.

He also was an adviser on the Republican presidential campaigns of former Governor Scott Walker of Wisconsin, former Governor Mitt Romney of Massachusetts and Senator Ted Cruz.

Earlier in his career, O’Brien was a senior legal officer for the UN Security Council commission that decided claims against Iraq that arose from the Gulf War. He was a major in the US Army Reserve.

O’Brien was among five job candidates Trump said on Tuesday were under consideration.

His previous national security advisers were HR McMaster, who was replaced by Bolton in March 2018, and Michael Flynn, who was fired shortly after taking the role and later pleaded guilty to lying to the FBI.