"He would leave -- and he'd have a right to leave," cautioned Graham.
"If he got two thirds of what he needs, which I think he's well on his way to doing, for us to steal from him is not going to help the party," he added. "You can lose an election. We've lost an election before. But what I'm trying to do is focus on the day after we lose. Can we rebuild this party? Can we create a form of conservatism that's enticing to young people and people of color? I think we can. And I think that's the only hope for the Republican Party and, quite frankly, one of the big hopes of this country."
Trump is potentially destroying the Republican party and exploiting race in his bid to secure the Republican presidential nomination, Graham says.
"He's trying to hedge his bets," Graham told CNN senior political commentator David Axelrod on "The Axe Files" podcast, produced by CNN and the University of Chicago Institute of Politics. "I don't think he supports the KKK. I don't think he's a racist. But he's playing a political game."
Asked by Axelrod before Trump's dominant showing on Super Tuesday if Trump is exploiting race for political gain, Graham replied, "Definitely. So far. But in the end it'll be the demise of Donald Trump and the Republican Party if we don't watch it."
Graham is no fan of one of Trump's top current rivals, Texas Sen. Ted Cruz. The choice between Cruz and Trump, he said recently, is like the choice between being poisoned or shot. After criticism of Trump for being slow to disavow the KKK, Graham essentially said he'd pick the poison and that the party might have to rally around Cruz to stop Trump.
He told Axelrod the GOP frontrunner is a "demagogue... playing on people's fears."
"Our party is about to fall apart," he warned. "Immigration is our undoing."
"There's two things underlying his campaign: if you elect me, I'm going to get rid of them who are taking your job and corrupting our way of life and I'm going to make us safe again and secure again. And if you elect me, I'm going to make sure the Chinese and other people -- foreign entities -- don't take your job away from you unfairly."
Trump's campaign is based on "xenophobia, race-baiting, and with just a tinge of religious bigotry," he added.
To hear the whole interview with Graham, which also touched on how his parents' owning a bar in a small South Carolina town prepared him for a career in politics and much more, click on http://podcast.cnn.com