John Bolton's departure as President Donald Trump's national security advisor comes after a rising number of rifts in which the arch-hawk was clearly at odds with his boss.
While Trump is accustomed to aides who race to accommodate every sudden policy turn, Bolton came with decades of experience in Washington and had little to lose by leaving his job.
Here are some of the key areas of disagreement:
- Afghanistan -
Trump dropped a bombshell on Saturday by saying that had invited leaders of the Taliban to Camp David, the presidential retreat, to discuss a deal on which the United States would withdraw thousands of troops from Afghanistan.
Such top-level negotiations would be anathema to Bolton, a strong proponent of deploying military force in both Afghanistan and Iraq under former president George W. Bush and a lifelong critic of concessions to adversaries.
The Washington Post reported that tensions had risen to the point that Zalmay Khalilzad, the US negotiator with the Taliban and another Bush veteran, refused to share his draft deal with Bolton for fear he would scuttle it.
Trump ultimately said he canceled the Taliban meeting, citing an attack that killed a US soldier, and said the talks were dead.
- Iran -
Bolton has long been a vociferous hawk on Iran close to its militant exiled opposition. In 2015, Bolton wrote an opinion piece in The New York Times bluntly headlined, "To Stop Iran's Bomb, Bomb Iran."
Shortly after Bolton took office, Trump walked away from a nuclear deal negotiated under his predecessor Barack Obama and slapped punishing sanctions, although Bolton stopped short of saying the United States was seeking regime change.
But Trump has increasingly said that he is open to diplomacy.
Trump appeared supportive of a French proposal to provide Iran an economic credit line and said that he is willing to meet President Hassan Rouhani without preconditions.
- North Korea -
Bolton is also well-known for his hard line on North Korea. Shortly before his appointment, he wrote in The Wall Street Journal that the United States would be justified in waging a pre-emptive strike on the country.
His criticism of the totalitarian state goes far back, with North Korea in 2003 calling him "human scum" after Bolton, than a State Department official, called then leader Kim Jong Il a "tyrannical dictator."
Bolton nonetheless joined Trump in two landmark summits with Kim in Singapore and then Hanoi, where he urged Trump not to agree to a deal without further commitments by Pyongyang.
By the time Trump arranged an impromptu third summit in June the Demilitarized Zone between North and South Korea, Bolton was spotted a safe distance away in Mongolia.
- Venezuela -
Bolton has championed one of Trump's biggest foreign policy pushes, seeking to topple Venezuelan President Nicolas Maduro, a leftist who presides over a crumbling economy.
But Bolton made his exit before Maduro, who remains in power and enjoys support of the military more than half a year after the United States and other major Western and Latin American powers declared him illegitimate.
Trump has been speaking less about Venezuela and, according to multiple reports, he chided Bolton in private for overselling the ease with which opposition leader Juan Guaido could take over.