Trump, who is running for reelection, regularly criticises Nato but launched his most extreme broadside yet in February, saying he would “encourage” Russia to attack members that had not met their financial obligations.
The comments prompted Nato secretary-general Jens Stoltenberg to urge him not to “undermine” members’ collective security.
The Republican former president’s attitude to Nato came up in an interview on British network GB News, when host Nigel Farage observed that critics had pointed to his Russia remarks to oppose the controversial tycoon’s reelection.
“They can use it – I don’t care if they use it – because what I’m saying is that’s a form of negotiation,” Trump said.
“Why should we guard these countries that have a lot of money and the US was paying for most of Nato?”
Trump, 77, has long complained about Nato, accusing the 28 European members in particular of not pulling their weight on military spending, taking for granted that they can rely on the US as a defensive shield.
But he has never demonstrated that he understands how Nato funding works, mischaracterising it instead as a club which subsists on membership fees.
In 2006, Nato countries made a vague commitment – formalised in 2014 – to spend 2% of their gross domestic product on their own defence, but members do not pay subscription fees and do not “owe” the alliance money for defence.
The benchmark is voluntary and there are no penalties enshrined in Nato’s founding treaty for falling short.
“I believe the US was paying 90% of Nato, the cost of Nato. It could be 100%. It was the most unfair thing,” Trump told GB News.
“And don’t forget, it’s more important to them than it is to us. We have an ocean in between some problems, okay? We have a nice big, beautiful ocean, and it’s more important for them.”
Beyond Nato, allies are also concerned about the US’ continued support for Ukraine, seen as vital to sustaining its war effort against Russia.
Trump – who often brags that he could end the two-year-old war on his first day in office – told GB News he would be able to negotiate with Russia’s president Vladimir Putin.
“I got along with Putin great… That’s a good thing, not a bad thing,” he said.