On a spring morning in 2016, the retired four-star general Mattis, who was forced out of his job by then-President Barack Obama, spoke before defence and foreign policy experts gathered just blocks from the White House. The 65-year old speaker, with silver hair and puffy eyes, was blunt. For all the dangers al-Qaeda and the Islamic State of Iraq and the Levant (ISIL, known as ISIS) pose in the Middle East, he warned that the Iranian regime "is the single most enduring threat to stability and peace". He recalled that as commander of US troops in the Middle East, the first three questions he would ask his subordinates every morning "had to do with Iran and Iran and Iran". Nine months later, James Norman Mattis returned to the US capital as defence secretary of President Donald Trump.