During a 2018 Russia-US summit in Finland, for instance, he disregarded US intelligence services, choosing to believe Putin’s denial of meddling in the 2016 election.

If Trump returns to the White House, this more positive attitude toward Russia — which is echoed in much of the Republican base and some of the party’s members in Congress — is likely to re-emerge as a driving force in US policy.

His comments at a CNN-hosted town hall event this week provided further evidence to those who accuse him of being too cosy with Putin.

The former president said he could end the war in 24 hours but did not say how. He refused to be drawn on whether he wanted Ukraine to prevail and complained about the cost of the military aid.

“We don’t have ammunition for ourselves. We’re giving away so much,” he said, accusing European countries of not contributing enough.

While the US Congress has approved billions of dollars in support for Ukraine to be distributed over an extended timeframe, as president, Trump could use his executive power to slow down or even stop that support.

He did this before when president, for some congressionally approved military aid.

Some of his Republican colleagues were quick to condemn his remarks, but it is possible — or even probable — that if Trump were elected in November 2024, US backing for the war effort could end entirely.

At the very least, the full-throated support for Ukraine that the current administration has expressed, along with its aggressive diplomatic efforts to maintain a united front with European allies on Russia sanctions, would in all likelihood be greatly diminished.

In the UK, which is ramping up its assistance to Ukraine to now include long-range missiles, there are concerns about the implications of a Trump presidency.

If Trump cuts off the supply of weapons, the war will end on Russian terms, which is the West’s worst nightmare, says the former head of Britain’s secret service, Sir Alex Younger.

“Putin didn’t have a Plan B when he invaded Ukraine but this is now his Plan B — to wait it out.”

Ukraine’s President Volodymyr Zelensky said his army needs more equipment ahead of counter-offensive

American public support for helping Ukraine has dropped since the start of the war and a Pew Research survey this week showed an increase in the number of Americans who believe the US should focus more on problems at home.

Jeffrey Treistman, a professor of national security at the University of New Haven in Connecticut, said it’s unclear whether withdrawing US assistance would end the war overnight — it could still grind on for years or decades.

“The Ukrainians to their credit have shown incredible resolve to fight the Russians and repel the invasion with minimal support initially,” he said.

“So it has the potential — even if the US were to stop providing assistance — of continuing and dragging on for the foreseeable future.”

If Kyiv is worried, they are not letting any anxiety show publicly. The day after Trump made his comments, Ukraine’s President Zelensky told the BBC he had no fears about the 2024 election.

Playing down the prospect of a weaker US-Ukraine relationship, he said: “I think that the elections in the US are in a year. Who knows where we will be. I believe that we will win by then. So we’ll see.”