Josh Barro/Business Insider
"You go live in Gaddafi's Libya," he said in a session at the Milken Global Conference. He was addressing Donald Trump, the Republican presidential frontrunner, who was not present.
In a February debate, Trump said: "We would be so much better off if Gaddafi would be in charge right now."
He has also said the United States would be better off with Saddam Hussein still leading Iraq.
"Isn't it too bad that we knocked him out in the first place?" he said in a recent Fox News interview.
"You want to be the leader of the friggin' free world, and you're yearning for dictators," Graham said Tuesday of his former GOP rival. "I'm a Republican, and my party has lost its way, in terms of the Donald."
In his criticism of the Republican frontrunner, Graham - who ran a campaign highly critical of Trump - also seemed to implicitly acknowledge Democratic frontrunner Hillary Clinton's prospects of winning in a theoretical general-election matchup against Trump.
"The next president of the United States, whoever she may be" will have to take on radical Islam, he said.
In the same session, former British Prime Minister Tony Blair did not directly answer a question about whether the current chaos in Iraq and Syria is a result of the American-British decision to invade Iraq in 2003. The two also went back and forth over their respective parties' troubles over the past few months.
"You're still a Republican, right?" Blair asked Graham. "I'm in the British Labour Party. We're hanging on in there, in our separate ways."
Like the Republican Party, Labour has suffered from public infighting in recent months, most recently over anti-Semitic comments by prominent party members.