What to know about Robert O'Brien, Trump's new national security advisor

12:21 PM ET Wed, 18 Sept 2019

President Donald Trump named Robert O'Brien as his national security advisor on Wednesday, eight days after the abrupt departure of John Bolton. O'Brien, a State Department official, will become Trump's fourth national security advisor, following the departures of Bolton and three-star Army generals Michael Flynn and H.R. McMaster.