During an appearance on a rightwing radio program, the hosts asked Trump about Putin recognizing two breakaway regions in eastern Ukraine as independent.

"I went in yesterday and there was a television screen, and I said, 'This is genius,'" Trump responded.

"Putin declares a big portion of the Ukraine -- of Ukraine -- Putin declares it as independent. Oh, that's wonderful."

Russia is facing an international backlash after Putin ordered his forces into Ukraine to secure the self-declared Donetsk and Lugansk rebel republics.

The move came with tens of thousands of Russian soldiers on Ukraine's borders and amid warnings of an all-out invasion.

Trump said Putin's tactics had been "smart" and argued, without elaborating, that the United States could replicate them on its border with Mexico.

He followed up with a separate statement arguing that the Ukraine crisis could have been averted altogether if it had been "properly handled" by President Joe Biden, who defeated him in the 2020 election.

"I know Vladimir Putin very well, and he would have never done during the Trump administration what he is doing now, no way!" the twice-impeached former president said.

Domestic firestorm

Trump, who had been largely silent on the escalating Russian threat to the US ally before Tuesday, criticized Washington's "weak" response which he said did not match Russia's actions. 

"Now it has begun, oil prices are going higher and higher, and Putin is not only getting what he always wanted, but getting, because of the oil and gas surge, richer and richer," Trump added. 

Former White House Russia advisor Fiona Hill told CNN Sunday that Trump's foreign policy had emboldened Putin. 

The former president had been driven by personal concerns rather than the national interest, she said.

"There's no Team America for Trump. Not once did I see him do anything to put America first. Not once. Not for a single second," said Hill, once one of Trump's most senior aides.

Ukraine found itself caught in a US domestic political firestorm when then-president Trump asked its leader to launch a spurious corruption probe into Biden's family ahead of the 2020 presidential election.

Accusations that Trump tried to block military aid to pressure President Volodymyr Zelensky sparked the first of the Republican's two impeachments.