President Trump and John Bolton's rocky relationship stretches back years and includes recent clashes over Bolton's criticism of Trump's summit with Vladimir Putin.

Trump, during that first term, was churning through national security advisers with regularity, and Bolton jumped from his role as a Fox News analyst to the White House in March of 2018 after promising Trump “he wouldn’t start any wars” if he was selected, CNN reported at the time.

An investigation seeks to determine whether Mr. Bolton illegally shared or possessed classified information, according to two people familiar with the case.