President Donald Trump emerged from the Marine One helicopter in Los Angeles, Wednesday, September 18, with Robert O'Brien, who Trump has named as his new national security adviser. O'Brien replaces John Bolton, a vigorous proponent of using U.S. military force abroad and one of the main hawks in the administration on Iran. 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.