Republican presidential candidate Sen. Lindsey Graham (SC) said in an interview with CNN on Tuesday that fellow candidate Donald Trump has tapped into the “dark side” of the GOP.

Graham was explaining how his rival has managed to dominate the Republican presidential race, polling as high as 35 percent depending on the survey. Graham said the support still represented a minority of the GOP.

“Twenty-five percent of our party that probably thinks Obama was born in Kenya or wants to believe that. There’s 25 percent of our party wants him to be a Muslim because they hate him so much,” Graham said. “So, there’s a dark side of politics that Mr. Trump is appealing to.”

Graham initially used the interview to defend his dismal poll numbers in his home state, South Carolina, but pivoted into a more specific attack on the GOP frontrunner. He said a Trump nomination would “kill” the GOP.

“The leader of our party has come up with a deportation plan that is Joseph McCarthy-like and he is saying things about Megyn Kelly and other women that are digging a big hole. And the chairman of our party said Trump was a net positive. Let me tell you, I think he’s hurting our party.”

He also said Trump’s plan to get rid of birthright citizenship was constitutionally unsound.

“He’s shallow. He’s ill-prepared to be commander in chief,” Graham said. “He doesn’t know what he’s talking about in terms of how our laws work. He says the worst things possible about immigrants and women. And he’s a complete idiot about Mideast policy.”

Trump’s strategy to defeat the Islamic State terrorist group, he said, was worse than President Obama’s, a strategy which which Graham has repeatedly voiced discontent.

Graham used some of his Southern charm to end the interview: “Come to South Carolina. I’ll beat his brains out.”