President Donald Trump made the announcement via Twitter. I informed John Bolton last night that his services are no longer needed at the White House. I disagreed strongly with many of his suggestions, as did others in the Administration, and therefore..., President Trump, Twitter. ....I asked John for his resignation, which was given to me this morning. I thank John very much for his service. I will be naming a new National Security Advisor next week, President Trump, Twitter. Bolton was Trump's third national security advisor. He is known for his hawkish stances on Iran, Afghanistan and North Korea, positions that often had him at odds with the president. Trump reportedly grumbled that Bolton seemed too eager for the U.S. to involve itself in another war. Who Trump is considering to act as his fourth national security advisor is currently unknown.