Irrespective of whether Iran is responsible for the recent attacks on Gulf shipping, the crisis now unfolding is fundamentally one manufactured out of thin air by the Trump administration. The implications go beyond the threat of a major war and consequent worldwide economic crash. Donald Trump’s reckless, incoherent Iran policy also throws into question the viability of the role of the United States as the global leader.

The US achieved its hegemonic status in the world system not simply through raw strength, but also by convincing the second-tier capitalist powers that it could manage that system in their interests as well as its own. Washington could be relied on to confront and put down challenges to the capitalist order, expand and deepen its reach, and handle crises as they arose. It was through responsible management of the system in the interests of western capital and state power more broadly (if not of humanity as a whole) that the US secured consent from its allies to lead this new form of empire.

The 2015 nuclear deal with Iran, brokered by the Obama administration and signed by the permanent five members of the UN Security Council, Germany and the European Union, was an example of this hegemony in action. The deal was only superficially about the always implausible threat that Iran would build a nuclear weapon and then use it in a suicidal attack on a US ally. The deeper strategic purpose was to bring Iran in from the cold, stabilise its relationship with the wider Middle East, and open it up as a market to international (principally European) capital. The promise of greater stability on their doorstep and a significant new global south market to exploit was a major prize for the European powers, delivered to them by a competent and responsible hegemon.

So, naturally, the Europeans have watched in horror as the Trump administration tore up the deal, ratcheted up sanctions on Iran with the apparent aim of collapsing its economy, and boosted Washington’s military posturing in the Gulf on the flimsiest of pretexts. A single purpose to this aggression is difficult to discern. Trump’s national security adviser John Bolton – a hawk so thuggish he makes Donald Rumsfeld look like Bertrand Russell – is openly in favour of regime change and comfortable with starting a war to that end. Trump – counterintuitively, and in strictly relative terms – is the dove in this equation, conscious of his election promise to end foreign wars, and seeking only to force Tehran into striking a better deal than his tormentor Barack Obama was able to make. Neither of them is likely to get what they want.

Trump seems to have no idea how to climb down from the perilous situation he has created

Trump and Bolton have only succeeded in provoking increased belligerence on Tehran’s behalf. Having seen its 2015 concessions rewarded with further punishment, and waited a year while Europe failed to mitigate the effects of US sanctions, the regime has now run out of patience. Its threats to finally pull out of the nuclear deal, and probable (though not certain) culpability for attacks on shipping in the Gulf, are likely designed to strengthen its hand in the stand-off, and based on the calculation that Trump does not want a war. There is a serious danger of this state of high tension breaking out into open conflict, through miscalculation or overreaction from either side. Trump seems to have no idea how to climb down from the perilous situation he has created.

Washington’s European allies are now faced with the opposite of what they thought they had won in 2015. Their exporters’ and investors’ hopes of an Iranian opening are dashed, and the Middle East is more unstable than at any time since 2003. A war in the Gulf would be a disaster far worse than that triggered in Iraq 16 years ago, with an effect on the oil price that would send a weakening global economy into a nosedive. Even if Trump is replaced with a Democrat in 2021, the Iranian regime will never trust the Americans enough to strike another bargain, which leaves the hardliners in Tehran strengthened, the moderates humiliated, and regional tensions more intractable as a result. European leaders might ask themselves what Washington would do differently if it were actively seeking to betray their trust and undermine their interests.

The temptation will be to wait for Trump to lose the 2020 election and for life to return to normal. But what if this is the new normal? The precedent of the 2003 invasion of Iraq, and the militaristic dogmatism of which that enterprise was born, suggests an emerging behavioural pattern. Far from being aberrational, Trump’s presidency fits with the Republican party’s long-term trajectory into unreasoning hawkish belligerence. The fact that tens of millions of Americans – mostly middle-class or affluent white people – were prepared to vote for a figure like Trump in 2016 demonstrates that this state of affairs cannot simply be wished away. With one of Washington’s two parties of government firmly in the grip of extremists, US allies will need to ask themselves if American leadership is now a reliable asset or a dangerous liability.

• David Wearing is a specialist on UK foreign policy in the Middle East