British prime ministers do not, as a matter of protocol, express preferred outcomes in US elections. But there is no convention limiting the number of times the question can be asked. It won’t go away while Donald Trump is a contender for the White House. A second Trump term can’t be brushed aside as the kind of hypothetical scenario on which leaders routinely withhold comment. Nor can it be cordoned off as foreign policy, which rarely influences UK general elections. Aside from being a menace to the US’s constitutional order, Trump is an eager vandal of his country’s historic alliances. He has threatened to pull the US out of Nato, and is reported to have said that he would not come to Europe’s defence if it came under attack. He is an admirer of Vladimir Putin. In trade and diplomacy, threat is his only negotiating tool. He thinks laws make no demands of him but can be used as weapons against rivals. Trump’s first term fractured the geopolitical settlement upheld by postwar institutions and rules-based clubs of (mostly) democratic states. A second term would shatter it. What remains of “the west” as a coherent concept would be dissolved in a sprawling transatlantic competition for the soul of European and American democracies. Parties committed to the defence of liberal constitutions would be traumatised, religious and ethnic nationalists emboldened. It may not happen. The election is 10 months away. But the mere possibility is reason enough to legitimately probe how a British prime minister would respond. The question is uncomfortable for Rishi Sunak and Keir Starmer in different ways. Sunak is not Maga material. His taste in American politicians is old-fashioned, establishment conservative. On a recent trip to the US, he took time to meet Mitt Romney, a failed Republican presidential nominee and outspoken Trump critic. He swerved a meeting with Trump himself. But Sunak’s party is steeped in Trumpian spirit. It has been blended and stirred into the Tories’ own Brexit home-brew since 2016, year of double ballot-box shocks on either side of the Atlantic. The subsequent evolutions of the two phenomena don’t track each other exactly. One thing they share is ignominious failure on a scale too profound for their supporters to accept, resulting in an intensified cult of denial and zealotry. It should surprise no one that Boris Johnson and Liz Truss have endorsed the Trump revival. Sunak has neither the courage nor much incentive to repudiate that tendency. Starmer has the opposite problem. Labour MPs, activists and supporters will be increasingly incensed by the monstrosity of Trump’s rhetoric and frustrated when their leader, invited to give a view, chooses diplomatic deflection over full-throated denunciation. It would be imprudent for a man who intends to become prime minister around the time of the US election to go on the record as a sworn enemy of one of the candidates. British interests require functional engagement with the White House regardless of who sits in the Oval Office. But it is also wise to anticipate only dysfunction with a president who despises the values that Starmer cites as his motivation for entering politics. The vindictive despot and the former human rights lawyer are not destined to enjoy a “special relationship”. The unavoidable consequence would be renewed focus on Britain’s relations with the rest of Europe. There would be an obvious alignment of strategic interests between an incoming Labour government and Europeans hungry for dependable allies. But Brexit is a powerful spoiler of obvious EU-UK common interests. The most effective features of the deal that Johnson’s former Brexit minister David Frost negotiated – the gifts it keeps on giving to Eurosceptics – are the way it automatically ratchets the two sides ever further apart and its lack of any mechanism for putting that conveyor into reverse. The trade and cooperation agreement (TCA) is the codification of the delusion that British prosperity demands regulatory divergence from the single market, coupled with a paranoid fear that any formal institutions for dialogue might be Trojan horses for reintegration. Anything that might one day facilitate cooperation in foreign policy, security, defence, energy, climate, migration – all the areas where it is rapidly becoming imperative that Britain and the EU collaborate – was ripped out of Theresa May’s Brexit model and ruled out of subsequent negotiations. Johnson gave away Britain’s seat on the board of a trading superpower in exchange for a hill of worthless sovereignty beans. Sunak has tacitly acknowledged that most businesses prefer alignment with the giant market on their doorstep to totems of regulatory freedom. A planned bonfire of retained EU law was doused. Measures that celebrated divergence for the sake of it – the return to imperial units, for example – have been scrapped. No leader of the current Tory party could openly question the ideological premises of the Brexit settlement and keep the job. A Labour one could, but Starmer has calculated that doing so too openly jeopardises his chances of becoming prime minister. The road to Downing Street passes through seats where even dry economic criticism of Brexit is misheard (or recast by Conservative campaigners) as a sneery disparagement of the people who voted for it. Within those constraints, Labour’s European policy contains only hints of ambition, some more credible than others. One track involves using a scheduled review of the TCA, due by 2026, to negotiate better terms. This approach is forcefully discouraged by Brussels insiders on the grounds that a mechanism intended to lubricate existing arrangements can’t be hijacked and turned into something else. More promising is talk of a UK-EU security pact, bringing some institutional scaffolding back to a relationship that currently consists mostly of ad hoc bilateral encounters. One message that diplomats and trade experts have repeated to Labour’s shadow team in private – and it appears to have sunk in – is that a new government can’t expect concessions to materialise out of pure relief in Brussels that Britain is no longer run by Tories. Another is that Brexit is not a problem for the EU in the way it is for Britain. Johnson’s deal is so bad from a UK perspective that, in terms of trade, it doesn’t leave much that Brussels could want from any renegotiation. But the calculus is somewhat different in the shadow of a Trump revival. The case for a more European Britain gets easier to make at home and the strategic promise of more Britain in Europe gains potential resonance in Brussels, Paris and Berlin. The year 2024 feels both a long way from 2016 and disturbingly like a sequel. The Brexit referendum asked a profound question about what it means for Britain to be a major European democracy outside the EU. Once we have left, what is the actual destination? The Tories have had eight years to supply an answer and delivered nothing but fantasy, fear and failure. It won’t be explicit in the campaign but this year’s general election asks the exact same question again. It is Labour’s turn to answer. Rafael Behr is a Guardian columnist