Such is the carnival of the Trump presidency, it can be tempting – especially for those outside the US – to view it as spectacle, a long-running reality TV show that veers between The Apprentice and House of Cards. But every now and then comes a reminder that, for all the cartoonish absurdity of the central character, the Trump administration is all too real, that its actions matter and that the stakes are lethally high.

A fresh and urgent reminder of that has come today with Iran’s declaration that it will no longer fully comply with the nuclear deal it reached with the US and Europe in 2015, by which Tehran agreed to a 15-year pause on its nuclear programme in return for the easing of economic sanctions. In a televised address this morning – exactly one year after Trump withdrew the United States from the deal – Iran’s president, Hassan Rouhani, announced a series of moves that would inch the country closer to acquiring the ability to produce nuclear weapons, moves that would only be averted if Europe defied Trump and allowed Iran once again to sell its oil and have access to the international banking system. For the most severe of these steps, Rouhani gave the Europeans 60 days to make up their minds: either resume trade or watch Tehran resume its nuclear efforts.

There’s no mystery why this has come about, even if cause and effect are separated by 12 months. On 8 May last year, Trump dismissed the advice of his own military and security chiefs and broke from what he called the “worst deal in history”. The likeliest explanation is that Trump disliked the deal not because it was ineffective – on the contrary, international inspectors were adamant that Iran was complying to the letter – but simply because it represented the single biggest foreign-policy achievement of his predecessor. Just as Trump has been determined to unravel Barack Obama’s healthcare reforms, so he has been bent on dismantling his international legacy. Laughable though it may seem, Trump’s envy and resentment of Obama and his reputation may well be the key driver of this major geopolitical shift.

The consequences have been direct. Fearing secondary sanctions imposed by the US – heavy US fines on any company that does business with Iran – European firms have pulled out of the country, choking an already ailing Iranian economy. That has led Iranians to demand their leaders hit back. The only surprise of today’s move is that it took so long, as Tehran waited a full year to respond to Trump – all the while continuing to obey the terms of the nuclear deal.

Make no mistake, none of this is to suggest Iran is some paragon. The opposite is true. Along with the Kremlin, the Tehran regime is a blood-soaked ally of Bashar al-Assad, shoring up his murderous rule in Syria. It is a prime funder of terror groups in the region. And its record in crushing domestic dissent is brutal and documented. (An Iranian man was hanged for the crime of having gay sex just a few months ago.)

The regime’s behaviour is abhorrent now and it was abhorrent when the nuclear deal was signed. That agreement did not make any false promises of making it better. All it pledged was to halt the country’s nuclear ambitions for the next decade and a half, to buy some time and open up the space for the kind of cooperation that might make change possible. Like it or not, Iran has kept its side of the bargain, which related solely to its nuclear conduct. By withdrawing from it without cause, it was Trump’s Washington, not Tehran, that behaved like a rogue state.

Now the Europeans face a painful dilemma. If they buckle to Trump, they will watch that limited but valuable 2015 agreement collapse. If they defy him, some of their biggest companies will face crippling fines. They have spent much of the last year trying to construct a mechanism to get around those US sanctions, without success. Perhaps now they will approach the task with more urgency, though it’s not as if European governments don’t have plenty on their plates. (This, incidentally, was an issue in which pre-Brexit Britain was centrally engaged: now, it seems, the country is too distracted and too diminished to have much diplomatic impact.)

Either way, what the Europeans and the rest of the world can no longer deny is that Trump’s antics – his resentments, his decisions based on impulse, rather than evidence, his constant gestures to the Fox News base – may play out like gripping TV drama. But they have consequences in the real world, and some of them are grave.

• Jonathan Freedland is a Guardian columnist