In a defining week for President Donald Trump on the world stage, national security adviser Robert O'Brien was a constant presence at the president's side as the U.S. edged to the brink of war with Iran and back again. The contrasts with O'Brien's predecessor along the way — in secret consultations at Trump's Mar-a-Lago resort in Florida, in the Oval Office and in basement deliberations in the White House Situation Room — could not have been more stark.
