The comments – made in an interview with a podcast supportive of him – sparked an immediate backlash as critics accused the 78-year-old Republican former president of being a "traitor" and an "idiot."

"Zelensky is one of the greatest salesmen I've ever seen. Every time he comes in, we give him $100 billion. Who else got that kind of money in history? There's never been [anyone]," Trump told the two-million-subscriber PBD Podcast.

"And that doesn't mean I don't want to help him, because I feel very badly for those people. He should never have let that war start."

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Trump – who is running against Democratic Vice President Kamala Harris – immediately pivoted to criticizing President Joe Biden, accusing him of having "instigated" the Ukraine war.

The Trump campaign told AFP the Republican was "clearly talking about Biden" and not Zelensky when he made his remarks about culpability for the war.

Ukraine communicates little about losses for fear of demoralizing its citizens after more than two years of Russia's invasion, but the Wall Street Journal reported last month that the war had killed or wounded a million soldiers on both sides.

The US is one of Ukraine's main backers, and has disbursed more than $64.1 billion in military assistance to Zelensky's government since the start of the war.

Although Kyiv is a US ally and Moscow is considered an adversary, Trump touted his good relationship with Russia's Vladimir Putin during a face-to-face meeting with Zelensky in September.

Trump was impeached for withholding vital weaponry from Ukraine after Russia's smaller-scale 2014 invasion, as he pushed its government unsuccessfully into announcing investigations into Biden, who was then his election rival.

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A federal investigation identified numerous links between the Trump campaign and the Russian government, which was found to have interfered in the 2016 US election on the Republican's behalf.

Criticism over Trump's apparent closeness to Putin was turbocharged last week by allegations that, while president, he sent the Russian leader Covid tests despite a US shortage and that the Republican and Putin may have been in contact numerous times since 2021.

"What a despicable Traitor," the Republicans Against Trump lobby group posted on X, alongside footage of Trump's podcast remarks.

"He's an idiot, and the whole world wonders why so many Americans don't see it," added national security analyst John Sipher, a senior fellow at the Atlantic Council's Eurasia Center.