Rightwing populists always promise they will get things done when they get into power. Immigration will be halted. Government waste will be eradicated. Traditional values will be revived. National decline will be halted. National greatness will be restored. Relations with the outside world will be redrawn.

Great tasks that, for decades, have been beyond the capability and will of conventional, compromising politicians will be accomplished – and fast. Populist governments will respond decisively to voters’ accumulated frustrations, cut through bureaucracy, and avoid the delays, U-turns and half-finished projects that usually blight democracies. The business of government will be straightforward and highly productive – even heroic – rather than complicated and disappointing.

From Donald Trump’s ultra-confident social-media posts to Nigel Farage’s sweeping pledges at press conferences, rightwing populism is never knowingly undersold. Yet, in office, its performance is rarely better than that of more orthodox ruling approaches, and often far worse. Look at Trump’s half-abandoned tariffs, backfiring war on Iran and barely implemented Gaza peace plan; Boris Johnson’s hollow promise of “40 new hospitals”; Brexit increasing rather than reducing red tape; some Reform-led councils raising rather than cutting taxes: over the past decade, rightwing populists in power have regularly done the opposite of what, or dramatically less than, they promised. In an era of suspicion and contempt towards politicians, how have they got away with it? And what might populism’s opponents do to make its failures count?

Paradoxically, the sheer number of failures helps underachieving populists in some ways, because each failure draws attention away from another. Like an office worker who has had too much coffee, Trump starts projects overconfidently, makes less progress than he expects, and then impatiently moves on to another one. Voters and journalists are left with the impression of forward momentum, rather than the reality of frequent false starts. While rightwing populism is often motivated by ancient grievances, on a day-to-day level it moves fast, and in these digitally accelerated times speed has a high social value, sometimes more than the actual completion of a task.

Rightwing populism is also at least as much about reshaping and controlling public discourse, and accumulating power, as achieving specific policy outcomes. Would a Reform UK government, faced with all the problems and limited resources of modern British governments, actually have the capacity to review the past five years of successful asylum claims, and then deport potentially hundreds of thousands of people, as the party proposed this week? For now, that may matter less to Reform than the fact that its announcement has given the ratchet of Britain’s immigration debate another twist. As Farage airily put it, when asked on Monday whether he planned to deport children, “We will come to the detail closer to the time, but this is about establishing the principle.”

Back when more voters expected governments to have concrete achievements – during the busy heyday of Blairism, for example – such vagueness from a would-be prime minister may have been highly damaging. Yet, after a decade containing four chaotic Tory administrations and an equally, if not always fairly, derided Labour one, and after even longer-running government fiascos such as HS2, much of the electorate and rightwing media believe that a messy, broad-brush populist regime couldn’t be any worse, and may be more dynamic and exciting. Joe Biden’s decline and incoherence in office similarly lowered the bar for Trump: making his increasingly erratic second term seem less strange and unacceptable, as though the presidency is routinely occupied by fading and stubborn old men. Soon, both the US and Britain, along with another once-revered democracy, France, will have no recent memory of stable government. For disruptive populists, that is a very helpful backdrop.

If their opponents want to break the cycle of ever more reckless rightwing policies and ever deeper irresponsibility, even nihilism, from some voters, then populism’s unique impunity in office needs to be ended. Forms of political messaging and campaigning need to be created and sustained that make populism’s failures in government feel more important to more people, and that connect these failures more clearly to populism’s fundamentals – its fantasies about restoring lost golden ages, its delusions that foreigners are always to blame. In short, populism needs to be held to account.

That is a big task, not least because powerful interests benefit from chaotic populist government: oligarchs hoovering up state contracts; traders who profit from instability; an ever more competitive media, desperate for clickable political content. But the shortcomings of other, more entrenched forms of government have been damagingly exposed before. During the postwar years, for example, the sometimes unrealistic promises and flawed or abandoned building projects of state-planned economies in both the west and the eastern bloc were highlighted so repeatedly by journalists, activists and politicians that, fairly or not, state planning and white elephants became synonymous. A similarly sustained attack could be mounted on rightwing populism’s governing record, so that it becomes much more widely associated with amateurishness, betrayals and incompetence.

So far, populism’s enemies have focused more on its extreme messages and disregard for democratic rules, an understandable approach for those who dislike extremism and believe in representative politics, but one that restricts the debate about populism largely to arguments about rhetoric and political process – controversies in which the movement’s loud, transgressive leaders are usually quite comfortable. It is in the less dramatic, more patient business of making government work where populist rulers tend to be less proficient and more vulnerable.

This week, the Trump administration finally began accepting applications for refunds from businesses that had paid tariffs, two months after the supreme court ruled the president had no authority to impose them. Through a specially created payment system, more than $160bn may have to be reimbursed to more than 300,000 companies. Two months is a long time in today’s feverish politics, and Trump’s huge court defeat has already receded behind the even larger and more recent Iran disaster, but its costs could run on for years. Paying proper attention to such complicated failures of populist government would be a big change for much of the media and many voters. But, without it, populism will probably get many more opportunities to do much worse.

• Andy Beckett is a Guardian columnist