New national security advisor Robert O'Brien speaks with US Presdent Donlad Trump (not shown) on September 18, 2019 at Los Angeles International Airport in Los Angeles, California. - Last week, Trump abruptly fired John Bolton, a vigorous proponent of using US military force abroad and one of the main hawks in the administration on Iran. O'Brien has until now served as Trump's envoy for situations involving US hostages abroad. He comes into the new job with backing from Secretary of State Mike Pompeo and senior Republicans in Congress. (Photo by Nicholas Kamm / AFP) (Photo by NICHOLAS KAMM/AFP via Getty Images)