Bolton is a leading foreign policy hawk and Trump’s third national security adviser. Bolton, who was also a chief architect of Trump’s strident stance against Iran, had advocated a tougher approach on North Korea, Iran, Russia and Afghanistan.
Bolton, who took up the post in April 2018, replacing H.R. McMaster, had sometimes been at odds with Secretary of State Mike Pompeo, one of Trump’s main loyalists.
Trump’s North Korea envoy, Stephen Biegun, is among the names floated as possible successors.