The decision of James Mattis to leave the post of US secretary of defence underscores a dismal truth about Donald Trump: that he governs just as he ran for office – as a producer of outrage rather than as a formulator of policy. Widely respected as a soldier and a diplomat, Mr Mattis had conveyed a sense of competence and good judgment in a White House plainly lacking in both. In deciding to leave, the four-star Marine general has created headlines and a sense of chaos. Unfortunately such a situation suits the volatile president. Mr Trump’s administration, like his campaign, specialises in manufacturing daily spectacles which scandalise, distract and, most importantly, polarise. The purpose is to summon the emotions of both supporters and detractors, and confirm their prejudices. The spectacle is designed to reinforce convictions about Mr Trump’s friends and enemies; it is not about policy.

Hence the president’s order to withdraw all 2,000 US troops from Syria within a month, and thousands from Afghanistan, has no rationale. It is not because Islamic State has been defeated in the Middle East. Nor is it because the job is finished in central Asia. Far from it. However, the move precipitates a crisis both at home and abroad. The United States is now prepared to abandon friends without warning. If the US does remove its troops from Syria, it will leave its allies – the Kurds – at the mercy of Turkish and Syrian forces, and embolden Russia and Iran, which have chafed at US power in the region. There may well be a dramatic shift in the balance of power in Syria, which has been mired in war for almost eight years. Similarly, Kabul’s authority rests in part on western troops. Mr Mattis rightly thought an American presence was necessary to overcome terrorists in both countries and provide the required clout to negotiate a lasting peace. Mr Trump’s foreign policy, by contrast, is a version of “hit and run” – attack enemies with overwhelming force and rush home, leaving others to clean up the mess.

Mr Trump had said he wanted to pull back from the US’s traditional pivotal role in supporting the global rules-based system. The US has long had a sense of exceptionalism. It undeniably sought a multilateral order to exercise a controlling influence over. Previous White Houses have sought to defend this aim, not unreasonably, on the basis of democracy, the rule of law and liberal values. Mr Trump is the first president of the postwar era who does not. Instead he expresses admiration for dictators.

Mr Mattis in resigning wrote pointedly that it was clear that China and Russia “want to shape a world consistent with their authoritarian model – gaining veto authority over other nations’ economic, diplomatic and security interests”. The implication is that in not confronting the authoritarian model, the US risks endorsing it. This is the real rebuke to Mr Trump, a narcissistic liar with a strong sense of mafia ethics. The president believes government should emote for his base rather than perform for all. His administration has increased inequality and backed voter-suppression measures. If unchallenged, US democracy risks being underpinned by rigged elections rather than political competition. Mr Trump promised disruption. The world ought to have no illusions about how much he is delivering.