A civil war over US military aid to Ukraine has erupted among Republicans, pitting foreign policy "hawks" against the isolationist right and setting the stage for the most consequential debate so far in the 2024 presidential election.

The fight over how much help to give the US ally in repelling Russia's invasion has intensified since presumed White House hopeful Ron DeSantis echoed a Kremlin talking point by likening the conflict to a "territorial dispute."

The Florida governor is arguing that Ukraine is not a "vital" national security interest, aligning himself with former president Donald Trump and cementing a profound shift in Republican thinking.

The two highest-polling potential Republican nominees are backed by Kevin McCarthy, the party's top lawmaker in the House of Representatives, which would have to support future funding.

McCarthy has opposed what he calls the "blank check" approach to Ukraine aid, but has stopped short of calling for a complete halt to payments.

Further to the right, failed Arizona gubernatorial candidate Kari Lake, seen as a rising star of Trump's populist "America First" movement, has railed against taxpayer dollars "being sent overseas to start World War III."

And South Dakota Governor Kristi Noem, another darling of the right who is being eyed as future White House material, said the conflict "should be Europe's fight, not ours."

Washington has sent Kyiv more than $110 billion in economic and military aid since the full-scale invasion began in February last year.

The isolationists' position chimes with most Republicans, according to an NBC News poll in January showing 63 percent opposing more funding and weapons for Kyiv.

But the electorate as a whole is much more pro-Ukraine, suggesting that any "America First" candidate emerging victorious from the Republican primary could face strong headwinds.

'Putin apologists'?

Republican strategist Ryan Williams argues that prioritizing funding for domestic issues over foreign adventures resonates with war-weary party supporters.

"That's why you're seeing more and more Republicans adopt that message, or at least tap the brakes on support for Ukraine, given where the base is heading," he told public radio station NPR.

Most mainstream Republicans however have warned that Russia's territorial ambitions would likely extend beyond Ukraine to NATO countries.

In contrast to the House leadership, top Republican senator Mitch McConnell has been an outspoken pro-Ukraine voice, and is seen as a bulwark against isolationism in the congressional party.

Trump's vice president Mike Pence offered a veiled criticism of his former boss, who sided publicly with Vladimir Putin over US intelligence after the Russian leader denied interfering in the 2016 US election.

"There is no room for Putin apologists in the Republican Party," said Pence, who is expected to join the contest for the Republican nomination.

Trump was also impeached in 2019 for withholding military aid to Ukraine while pressuring President Volodymyr Zelensky to help him dig up dirt on his election rival Joe Biden.

Former US ambassador to the UN Nikki Haley, Trump's only declared high-profile challenger, has said a Ukrainian victory would ensure a wider war was avoided.

"President Trump is right when he says Governor DeSantis is copying him," Haley said in a statement. "Republicans deserve a choice, not an echo."

Senator Lindsey Graham, who has endorsed Trump over fellow South Carolinian Haley, rejected DeSantis's characterization of the invasion as a territorial conflict, calling it "a war of aggression."

He and former New Jersey governor Chris Christie, early Trump rivals in 2016, both likened DeSantis's comments with British prime minister Neville Chamberlain's appeasement of Adolf Hitler.

© Agence France-Presse