Nine months is a long time to hold your breath. The identity of the next US president won’t be known until 6 November, but already the prospect of it being Donald Trump has America’s allies clenched in strategic suspense. In European democracies, the fear is existential. For 75 years, their security has been guaranteed by the North Atlantic treaty, which Trump scorns as a bad deal for the US. At a rally over the weekend, the former president boasted of having encouraged Russia to “do whatever the hell they want” to countries that weren’t, in his view, paying their Nato bills. If returned to the White House, Trump might not actually renege on US commitments of mutual assistance to countries that fear they are in Vladimir Putin’s firing line. But the former president doesn’t have to mean exactly what he says, or even win the election, for his words to have effect. Ambiguity undermines deterrence. American unreliability will permeate every discussion when Nato defence ministers gather in Brussels this week. The gripe that Europeans free-ride on America’s defence budget is an old refrain. Most Nato members accept it is also a fair one. Only a minority have met the commitment made in 2006 to allocate 2% of GDP for defence spending. But in the past, frustration at the asymmetry of contribution has been softened by historical allegiance and alignment of values. Even in terms of self-interested realpolitik, Washington could value the upkeep of European democracy, stability and prosperity as a Nato dividend. Not Trump. He doesn’t do alliances, only transactions and threats. Mutual benefit is for wimps. The test of a good deal in Trumpworld is that the other party feels cheated. For that reason he despises the EU even more than Nato because it isn’t a US client. It has its own commercial heft as a continental trading bloc. The ambition to spike Europe’s guns as an economic superpower is another thing Trump has in common with Putin. It is why they were both enthusiasts for Brexit. US unreliability is already stalking the battlefield in Ukraine. Vital aid has been held up in Congress, which is partly the effect of Trump having a thumb on the military scales before he has even been formally nominated as the Republican candidate. It looks like payout for a Kremlin bet that western finance and moral support for Kyiv will run out faster than Russian shells and conscript cannon fodder. There is a faction of the US right that admires Putin on ideological grounds, as a scourge of degenerate liberalism. But mostly Republicans are just glad if the war goes badly for the side Joe Biden has backed, so they can cast his presidency as an era of US weakness and Trump as a restoration of strength. The repugnant cynicism of that game will poison America’s international relationships, even if Biden wins a second term. It is already clear that the old congressional consensus in favour of constitutional democracy and the rule of law has gone. Seeing the writing on the wall, European leaders are talking with new urgency about what Emmanuel Macron calls “strategic autonomy”. This used to be dismissed as an improbable flight of Gallic fancy. Now it frames the continent’s agenda. The implications in terms of where the extra money for bigger defence budgets – even more than 2% of GDP – will come from, and what a consolidated continental defence capability actually involves, are only slowly seeping into domestic politics. Those questions are coming to Britain, too. It is a conversation for which Westminster is hopelessly unprepared. The proximity of a general election has narrowed horizons in what is at the best of times a myopic political culture. Foreign policy rarely impinges. Even when Brexit was the dominant issue, the focus was usually parochial – internecine Tory squabbles and nationalist mythomania, never a rational discussion of what it meant for the UK’s alliances. One sign that Rishi Sunak is sensitive to the magnitude of what might happen to the US in early November is that he is reported to be going off the idea of holding a UK ballot at the same time. Trump winning while parliament was dissolved would exacerbate the shock and complicate Britain’s response. But Sunak won’t be drawn on the deeper questions that should inform the response. David Cameron went so far as to describe Trump’s trolling of Nato over the weekend as “not a sensible approach”. That is, presumably, also the current prime minister’s view. Sunak brought his predecessor back into the cabinet so he could outsource foreign policy in an election year. His own diplomatic repertoire is thin. The main achievement has been stabilising EU relations via cordial and realistic engagement with Ursula von der Leyen, European Commission president. Bilateral European relationships have been neglected. Sunak still hasn’t visited Berlin since moving into No 10, which comes across as a snub given the importance of protocol in German politics. He has been to Paris, prompting reports of a budding bromance with Macron. But there is no substance to the partnership. The French president expected a high-level exchange of geopolitical analysis. His British counterpart wanted a quickie deal on stopping small boats crossing the Channel. The obsession with maritime migration has been more fruitful as bonding material in relations with Giorgia Meloni, the Italian prime minister with a pragmatic streak belying a far-right pedigree. It is a revealing affinity for Sunak, putting him closer to the camp of European populists who will cheer a second Trump term than the liberals who flinch at the thought. The preference is noted in Paris and Berlin. It is consistent with the tenor of Sunak’s plans to legislate Britain out of its treaty obligations towards refugees. The safety of Rwanda bill, under scrutiny in the House of Lords this week, repudiates less of the European convention on human rights than many Tories would like, but it is conceived in contempt for the court that adjudicates breaches of that convention. It implies that international law should melt under the heat of a government’s impatience to deport unwanted foreigners. The spirit is Trumpian. In other contexts, Sunak aspires to be a friend to Europe. His support for Ukraine is unwavering. He negotiated the Windsor framework for Northern Ireland in repudiation of Boris Johnson’s vandalistic Brexit method. But refraining from sabotage is the minimum requirement for functional relations. Good neighbourliness is a mood, not a policy concept. It doesn’t answer the hard question of how Britain engages with a Europe that craves strategic autonomy. For a generation, Britain’s foreign policy had two pillars – the EU and the transatlantic alliance. London was the pivotal bridge between Washington and Brussels. Brexit blew up one side. Trump has wired the other side for detonation. That is a crisis of Britain’s global orientation that should be central to debate in a general election campaign. But that would require political leaders who can admit the crisis exists. I’m not holding my breath. Rafael Behr is a Guardian columnist