An encounter between Keir Starmer and Joe Biden should be a meeting of minds. The British and US leaders’ global perspectives are neatly aligned, as happens from time to time in a way that makes the transatlantic “special relationship” more than a diplomatic platitude. But the political cycles are out of phase. Starmer is victorious, ascendant, new. Biden looks beaten by age.

The US president’s decline, painfully exposed in his recent TV debate against Donald Trump, has stirred panic in a Democratic party that needs a more dynamic candidate to fight November’s election. The same anxiety, less openly expressed, will swirl around the gathering of Nato leaders that brings Starmer to Washington for his first international fixture as prime minister.

The summit celebrates 75 years of the North Atlantic treaty. Biden is six years older than that. When elected four years ago, he embodied the restoration of US engagement with Europe along lines drawn in the 20th century – loyal to allies, preferring elected governments to tyrants. Trump’s priorities are the reverse. “America is back,” Biden declared to the Munich conference in 2021. Friends of US democracy, liberalism and the rule of law breathed sighs of relief.

It turned out to be a nostalgic interlude. Trump is only three years younger than Biden, and hardly a model of cognitive agility. Yet he is also the figurehead for a radical nationalist movement that claims ownership of America’s future with more confidence than liberal defenders of the constitution can summon.

That imbalance of energy – moderates looking haggard, besieged by preening demagogues – is present also in Europe. In France, the far-right National Rally has been held in check by an expedient and unstable voter coalition. The new balance of forces in parliament paralyses Emmanuel Macron’s presidency. In recent European parliament elections in Germany, Chancellor Olaf Scholz’s Social Democrats were beaten into third place by the far-right Alternative für Deutschland. Scholz’s coalition government looks doomed going into federal elections next year.

The picture across Europe is more nuanced than is portrayed by the gloomier accounts of encroaching fascism, but even when the liberal centre holds it looks defensive. It appeals to values and norms of a postwar western order that retains a moral purchase on some voters but doesn’t promise much by way of future material improvement. No one has found a durable way to turn the negative imperative of resisting extremists into a positive case for moderation.

In that context, Starmer will be greeted in Washington like a fresh-legged sub joining the pro-democracy team in extra time. After years of turmoil and Trumpesque posturing under the Tories, Britain bounds back into the global arena with a centre-left leader in total command of party and parliament. Britain has gone overnight from being a case study in political dysfunction to a laboratory for democratic rehabilitation.

Starmer’s majority gives him immense latitude to govern as he pleases, but the cushion of public goodwill is thinner. Change was the promise that sealed the electoral deal, and if that isn’t made tangible, the anti-incumbent tide that swept the Tories away will turn for Labour too in time.

Nigel Farage didn’t advance his mission to eclipse the Conservatives as far as he would have liked, but Reform came second to Labour in 98 seats. Its leader has a parliamentary platform and friendly media amplification – assets he is adept at exploiting.

Starmer has been explicit in his ambition to restore faith in conventional politics, refuting with competent government the despair and cynicism that give Farage’s anti-Westminster routine its traction. The proposed method is economic growth. Rachel Reeves – Britain’s most interventionist chancellor since the 1970s – will conjure up new prosperity and marshal it in the service of industrial and social renaissance.

The prime minister doesn’t advertise that intent with lofty rhetoric. It isn’t an idiom he finds comfortable and he thinks a jaded public, wary of all politicians’ promises, doesn’t want to hear it. When charged with running an overly cautious election campaign, Starmer responded that he was in the business of “credible hope, deliverable hope, making the change that will be material for people’s lives”. He means to do his talking on the pitch.

The obvious risk is that the economy doesn’t grow fast enough. Then there won’t be enough money for investment that might yield a Labour-branded feelgood factor. A symptom of voter disaffection with politics is unwillingness to be patient and extend the benefit of the doubt when progress is slow in coming.

Another hazard is that economic gains, if they materialise, don’t translate into public gratitude. Here the malaise afflicting Biden’s re-election campaign offers a salutary warning, beyond his doddering appearance. The US economy has performed well since Trump was ejected from office, yet hyper-partisan Republican voters believe the opposite is true. US unemployment is the lowest it has been for 54 years. The incumbent president gets no credit.

Biden’s industrial subsidy programme, channelling hundreds of billions of dollars into clean energy programmes and rustbelt rehabilitation, has been an inspiration to Reeves. But if the full might of the US treasury can’t procure electoral reward for the Democrats, what chance does its underpowered, fiscally pinched counterpart in Britain have of buying Labour loyalty?

Party strategists are rightly exercised by this problem. They have been sharing an article, published last year in the US journal Democracy, titled The Death of “Deliverism”. It argues that, while economic insecurity fuels populism, wealth redistribution is not an adequate antidote.

Once people have been made angry and unhappy by a dysfunctional economy, and channelled that rage into nationalist grievance, infusions of cash alone don’t make them happy and liberal. They also crave feelings of connectedness, belonging, respect. Economic growth can blunt populism, but it takes an emphasis on “identity, emotion and storytelling” to convert voters to a rival political prospectus.

It is reassuring that people close to Reeves and Starmer are pondering that lesson from the US. It is worrying that neither the prime minister nor the chancellor has a knack for narrating their political journey in ways that make an emotional connection with voters.

Perhaps they will get better at it. Starmer already sounds more relaxed in office than he did in opposition. He looks more comfortable on the field than complaining from the stands. Maybe there will be an economic boom so resounding that voters actually thank the government.

With the Tories in disarray and Reform on the parliamentary fringe, there is some space to practise competent administration, hoping that the benefits speak for themselves.

It is a hope shared by sympathetic politicians and besieged governments on both sides of the Atlantic. Now that Biden’s reign looks like mere respite between Trump terms, no one dares believe that insurgent nationalism is quelled in a single election victory. But Starmer will be welcomed to Washington as a leader who brings moral reinforcement to the cause.

• Rafael Behr is a Guardian columnist