US media named Ryan Wesley Routh, who was interviewed by AFP in Kyiv in 2022 where he had travelled to support the war effort, as the suspected would-be assassin of Donald Trump.
US media said it was Routh, 58, who was arrested after US Secret Service agents "opened fire on a gunman" carrying an AK-47 style rifle near the boundary of Trump's Florida golf course where the former president was golfing on Sunday.
The suspect had bolted out of the shrubbery he had been hiding in and escaped in a black car before he was tracked down by authorities.
Trump had no public events on his schedule for Sunday and his golf game was a last-minute addition to his itinerary, two sources familiar with the matter said.
Both CNN and CBS reported Routh was a self-employed affordable housing builder in Hawaii who had an arrest record spanning decades and regularly posted on politics and current events, including sometimes criticizing Trump, the Republican presidential candidate.
One cause Routh expressed support for was Ukraine's fight against the invasion launched by Russia's President Vladimir Putin.
"I am willing to fly to Krakow and go to the border of Ukraine to volunteer to fight and die... Can I be the example We must win," Routh said in an X post in March 2022, according to the New York Times, which also interviewed him.
AFP interviewed Routh in Kyiv in late April 2022, while he was taking part in a demonstration in support of Ukrainians trapped in the port city of Mariupol.
"Putin is a terrorist, and he needs to be ended, so we need everybody from around the world to stop what they are doing and come here now," he told AFP at the time.
The United States has been a staunch support of Ukraine since Russia invaded in February 2022.
The state of Florida has launched its own probe, according to its governor, into the incident.
"The people deserve the truth about the would be assassin and how he was able to get within 500 yards of the former president and current GOP nominee," Republican Governor Ron DeSantis said.
President Joe Biden will be replaced next January either by his Vice President Kamala Harris, who has indicated she will continue his policies of backing Ukraine, or by Trump, who would not say at a debate earlier this week whether he wanted Kyiv to win the war.