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“[Mr Putin] has taken over a country for $2 worth of sanctions. I'd say that's pretty smart,” Mr Trump said at a Take Back Congress Candidate Forum hosted at the resort in Palm Beach, Florida on Wednesday night.
“He's taking over … literally a vast, vast location, a great piece of land with a lot of people and just walking right in.”
Mr Trump claimed the invasion would have never happened "in a million years" if he were still president because he knows Mr Putin "very well".
Mr Trump said in another statement on Wednesday: “Putin is playing Biden like a drum. It is not a pretty thing to watch!”
Russia launched a full-scale invasion of Ukraine in the predawn hours of Thursday in one of the largest assaults on a European country since the Second World War.
The former president's late-night remarks were the second time this week he has praised the Russian leader.
On Tuesday, he complimented Mr Putin's “savvy” during an interview on the Clay Travis & Buck Sexton Show.
“I went in yesterday and there was a television screen, and I said, 'This is genius.' Putin declares a big portion of the Ukraine — of Ukraine — Putin declares it as independent. Oh, that’s wonderful,” Mr Trump said.
The former president was impeached for the first time in 2020 for reportedly pressuring Ukrainian President Volodymyr Zelenskyy to investigate then-presidential candidate Joe Biden and his son, Hunter Biden.
Mr Trump tied military aid to Kiev to the government digging up information that would help his electoral chances, a former White House official claimed in 2019.
The former president's comments are markedly different from most Republican politicians who, in a rare moment of bipartisanship on Capitol Hill, have condemned Russian aggression.
Among those attending the Mar-a-Lago event were Republican senators Ted Cruz and Lindsey Graham.
“The world needs to condemn Putin’s destruction of a neighbouring democracy as a war crime,” Mr Graham said in a tweet on Wednesday night.
Mr Graham was one of 20 members making up the US delegation to the Munich Security Conference, which took place last week.
“No matter what happens in the coming days, we must assure that the dictator Putin and his corrupt oligarchs pay a devastating price for their decisions,” the delegation said in a statement on Monday.
Mr Cruz, a frequent critic of Mr Biden, said the US and Ukraine would work together to hold Mr Putin accountable for the invasion.
But while Republicans mostly broke from Mr Trump in condemning Mr Putin, they appear to be more united in criticising the Biden administration for its handling of the crisis.
“Sadly, President Biden consistently chose appeasement and his tough talk on Russia was never followed by strong action,” House Republican leadership said in a joint statement, and added that the US president should levy even harsher sanctions on Russia.
Mr Graham this week called the White House's response “inadequate”, saying Mr Biden is “not seizing the moment".
Mr Biden this week announced his administration's first series of sanctions against Russia, cutting Moscow off from western financing and imposing sanctions on Russian oligarchs and their families. He is expected to announce additional sanctions on Thursday.