In response to Trump’s comments, NATO Secretary-General Jens Stoltenberg warned that any attack on the alliance would be met with a “united and forceful response.”

“Any suggestion that allies will not defend each other undermines all of our security, including that of the US, and puts American and European soldiers at increased risk,” he said.

“I expect that regardless of who wins the presidential election, the US will remain a strong and committed NATO ally.”

Polish Defence Minister Władysław Kosiniak-Kamysz also hit back, writing on social media: “NATO’s motto ‘one for all, all for one’ is a concrete commitment… No election campaign is an excuse for playing with the security of the alliance.”

And European Council President Charles Michael warned: “Reckless statements on NATO’s security and Art[icle] 5 solidarity serve only Putin’s interest. They do not bring more security or peace to the world.”

Trump’s latest South Carolina rally took place two weeks before the Republican primary contest in that state, where he remains the overwhelming favourite to beat his only remaining rival, Nikki Haley.

But the comments suggesting Russia should attack US allies who don’t pay their share were only some of the former president’s scaled-up rhetoric over the weekend.

Days after Republicans sunk a once bipartisan bill designed to stem the number of migrants illegally crossing the US-Mexico border, Trump highlighted his own plan to tackle the crisis.

“On day one, I will terminate every open border of the Biden administration, and we will begin the largest domestic deportation operation in American history,” he said as the crowd roared.

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According to his advisers, such a program would involve rounding up undocumented immigrants already in the US – many of them in sanctuary cities such as New York, Washington DC and Chicago – and placing them in detention camps to await deportation.

Earlier his speech, Trump bragged about how Republicans “crushed crooked Joe Biden’s disastrous open border bill.”

Had the bill passed last week, it would have given US authorities the power to bar migrants from crossing the border if crossings rose above 5000 on average per day on a given week, or 8500 in a single day.

It also included provisions to raise standards for asylum screening and deliver swift deportation for people who don’t qualify.

The former president also received enthusiastic cheers when he told the crowd that if elected, he would sign an executive order to cut federal funding “for any school pushing critical race theory (which examines systemic racism in American public policy), transgender insanity, and inappropriate racial, sexual, or political content onto the lives of our children.”

“It’s hardworking patriots like you who are going to save our country,” he told the mostly white crowd in South Carolina, a state with a dark history of slavery, and where black people now make up one in four residents.

“We will fight for America like no one has ever fought before. 2024 is our final battle.”

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