Donald Trump emerged from political exile Saturday to blast President Joe Biden and NATO over the Ukraine crisis and reprise his false claims of a stolen 2020 election in a speech to grassroots Republicans.

Speaking at the annual Conservative Political Action Conference in Orlando, Florida, the former president spent 86 minutes reprising many of his favorite applause lines, assailing the "radical left" and its "witch hunt" against him.

As massive explosions lit up the sky over Ukraine's capital Kyiv, Trump blamed Russia's invasion of its neighbor on Biden's "weakness" and lavished praise on President Vladimir Putin's intellect.

"As everyone understands, this horrific disaster would never have happened if our election was not rigged," he said, to rapt applause.

NATO, he said, was "looking the opposite of smart" for hitting Russia with sanctions rather than resolving to "blow (Russia) to pieces -- at least psychologically."

"The problem is not that Putin is smart, which of course he's smart," he went on. "But the real problem is that our leaders are so dumb."

After a year largely out of the public eye, Trump's ecstatic reception left little doubt that the Republican Party remains in thrall to the twice-impeached, single-term president.  

There were chants of "four more years" from the sea of supporters in red "Make America Great Again" hats, who clapped on cue as Trump railed against "woke tyranny" and "cancel culture."

The crowd reserved their largest cheers for the 75-year-old headliner's dismissal of Democrats' claims to be the party of democracy as "bullshit" -- and for his claim that Facebook founder Mark Zuckerberg "used to come to the White House and kiss my ass."

There were nods to a possible 2024 run -- "we did it twice and we'll do it again," he claimed, falsely recasting his 2020 defeat to Biden as a victory -- although he left the crowd guessing about whether he will personally challenge Biden to a rematch.

- 'Fight like hell' -

CPAC, the country's largest conservative gathering, usually offers a valuable insight into the direction the Republicans plan to take over the coming months.

Trump had been expected to lay out a forward-looking "vision for America," according to organizers, as the Republicans look to take back control of Congress in November's midterm elections.

Instead he dwelt at length on his 2020 election loss and his false claims that he was robbed by widespread voter fraud, urging the crowd to "fight like hell" or face their country being destroyed.

It was similar to the rhetoric that inspired a mob of his supporters to storm the US Capitol on January 6 2021, for which he was punished with his second impeachment. 

His remarks came as Russian rockets began pounding the outskirts of Kyiv in an escalating crisis that ended up emerging as a major topic of discussion at CPAC.

Trump called besieged President Volodymyr Zelensky "a brave man," falsely claiming that the Ukrainian leader had exonerated him over the scandal that led to his first impeachment.

While he was president, Trump withheld vital military aid from the US ally as he tried unsuccessfully to pressure Zelensky into digging up political dirt on the Biden family ahead of the 2020 election.

"After spending four years selling out Ukraine, the defeated former president took the stage at CPAC to double down on his shameless praise for Putin as innocent Ukrainians shelter from bombs and missiles at the hands of Russia," Democratic National Committee spokeswoman Adonna Biel said after the speech.