And then we haven’t even talked about the growing crisis among Democrats over Joe Biden’s fitness for office.

To the extent that they can assess a changing political landscape, European diplomats infer that Trump, a convicted felon, is now increasingly likely to serve a second term — a prospect that could herald a new period of American isolationism.

This divides Europeans into three camps: optimists, particularly the British and Germans, who say a Trump 2.0 presidency would be amenable to well-thought-out European convictions; skeptics, such as French President Emmanuel Macron, who argue that it is high time to Trump-proof Europe by shoring up its own security; and a third group, now much larger than in 2017 and embodied by Hungarian President Viktor Orbán, who is absolutely eager for Trump to become president and for the war in Ukraine to end, partly on Vladimir Putin’s terms.

There is a risk that these European divisions will lead to incoherence, making it easier for America to strike beneficial bilateral deals with individual nation states.

The US and Europe had a series of economic and security conflicts during Trump’s first presidency, but the war in Ukraine – which began in 2022, after he left office – has introduced a deadly ingredient that could cause a deep rift in transatlantic relations.

It is striking that the broad camp that believes Trump can be persuaded on Ukraine refuses to see the vice presidential nomination of J.D. Vance — an outspoken critic of US aid to Kiev who has been praised by Russian Foreign Minister Sergei Lavrov as “a man of peace” — as the end of discussions with the potential administration.

Speaking on the sidelines of the Republican National Convention, British Ambassador to Washington Karen Pierce said: “What we are talking about is not just security in Ukraine, but also for NATO partners. If Putin wins in Ukraine, that emboldens China, which has direct implications for the US.

“It also sets European security back 30 years, back to the fall of the Berlin Wall, and I don’t think anyone wants that, and I don’t think the next administration wants its entire term to be dominated by that loss of Euro-Atlantic security,” she told an event hosted by Politico.

Urban Ahlin, the Swedish ambassador to Washington, was also clear about the stakes. “We realize that Russia is an existential threat. If we don’t stop them in Ukraine, they will continue and pose a threat to the United States. In terms of costs, the costs will be much higher if we don’t stop the Russians now.

“If the US wants to save money, the right way to do it is to help the Ukrainians win this war. If Russia wins this, it will embolden other countries… North Korea, Iran, China. It will not stop in Ukraine.”

Polish Foreign Minister Radosław Sikorski struck an optimistic tone at a meeting at Chatham House, saying he had gathered from his conversations with Republicans that “there are two trends within the party and one is that it is not Ukraine that needs to be brought to the negotiating table, but Russia”.

He said Putin misjudged US policy, just as he had misjudged the EU and Ukraine, if he expected Trump to concede.

In what he described as the “not entirely unthinkable scenario” in which Trump refuses to provide further financial aid to Ukraine, Sikorsky said: “I think they will still sell us weapons for money and then we have a choice: do we step up our game or do we give up Ukraine?”

He pointed out that at extremis, there were $300 billion (£230 billion) in frozen Russian central bank assets in Belgium that Europe could use to buy weapons for Ukraine – a move that would face fierce resistance on the continent, not least from Christine Lagarde, the president of the European Central Bank.

Despite such optimistic voices, the reality is that there is no scenario between now and January, and no change in defence resources, that will not see Europe become dependent on the US for its security.

Senate Minority Leader Mitch McConnell may have been booed at the Republican convention, but this month he said he saw an “improved” political situation for Republicans when it comes to Ukraine. He noted that no incumbent who endorsed Kiev had lost a primary this cycle.

Observers note that a further reason for optimism is that two of McConnell’s potential successors as Republican Senate leader — Minority Whip John Thune and John Cornyn — still support Ukraine. McConnell has even vowed to make stamping out the “isolationist” strain of Republicans in the Trump era a top priority for his final two years in the Senate.

Vance’s nomination has particularly unsettled Germany. He has not only denigrated Germany’s dependence on the U.S. defense shield, but also attacked the country’s economic policies.

“You (Germany) are deindustrializing your own country, while at the same time saying that Putin must be defeated at all costs,” he said at the Munich Security Conference in February. “If Putin must be defeated at all costs, then, dear German friends, stop deindustrializing your own country in the name of a ridiculous green energy policy.”

Should the Trump administration indeed impose trade tariffs, as it has threatened, the re-appointed President of the European Commission, Ursula von der Leyen, already has a counter-strategy ready, based on the importance of the internal market for the US.

Total US investment in the EU is four times higher than in the Asia-Pacific region. EU foreign direct investment in the US is about 10 times higher than EU investment in India and China combined. A trade war would be disastrous for both sides.

Macron’s thinking holds that if Trump-style populism is not to spread across Europe, it must be fought, not flattered. That requires an unprecedented level of defense coordination across the continent.

Benjamin Haddad, a French member of parliament close to Macron, wrote on X: “The nomination of JD Vance as VP is another example: Trumpism has definitively triumphed among Republicans, and with it nationalism, rejection of alliances (starting with NATO) and support for Ukraine, protectionism. The conservatism of Reagan and Bush is dead and buried.”

Haddad also blamed Biden for implementing a series of isolationist measures to the detriment of Europe, warning: “Things will get worse after him. Trump’s lead in the polls, the underlying trends among post-Biden Democrats and the violent polarization of the American political debate should be a wake-up call for Europeans. We are alone in a more competitive and fragmented world.”

The difficulty for the Macron school is that the French president’s domestic political crisis is reducing his influence on how Europe responds to Trump. That has led many think tanks to predict that the European response will not be as unified as the first time around, even though the stakes are potentially higher.

Nathalie Tocci, director of Italy’s International Affairs Institute, said this week: “It is not necessarily clear that the political effect of a second Trump administration will have the same unifying impact on Europe as it did eight years ago. It is a much more politically fragile Europe.

“We’ve been having the Putin-Trump conversation for almost a year now. How are we going to coordinate ourselves? How are we going to prevent a rather indecent show where several Europeans flock to Washington to kiss the ring.

“Do we have a strategy? It’s the kind of thing that doesn’t require a lot of preparation. As far as I know, there isn’t one.”