Sen. Lindsey Graham told "Axios on HBO" that Donald Trump has a "dark side" but he tries to "harness the magic" because he succeeded where Republican candidates like John McCain and Mitt Romney failed.

Why it matters: The South Carolina Republican gyrates between support and criticism of the former president, even after Trump harshly criticized McCain — Graham's longtime friend — and helped spark the Capitol insurrection.

• "What I'm tryin' to do is just harness the magic," Graham told Axios' Jonathan Swan. "To me, Donald Trump is sort of a cross between Jesse Helms, Ronald Reagan and P.T. Barnum."
• "He could make the Republican Party something that nobody else I know can make it. He can make it bigger. He can make it stronger. He can make it more diverse. And he also could destroy it," Graham said.

The big picture: Graham won reelection in November in one of the most expensive political races in American history. That helps explain his embrace of Trump, wildly popular with the Republican base, but also confounds those who wonder why he sticks with him.

• In 2016, when they were competing for the GOP presidential nomination, Graham questioned Trump's mental fitness.
• After Trump beat Hillary Rodham Clinton, Graham embraced the new president, despite him criticizing his former sidekick McCain for becoming a prisoner of war in Vietnam.
• The day after the Capitol siege, Graham blamed Trump for fueling the attack and declared, "enough is enough."
• Now, Graham says he is reengaging purposefully.

What they're saying: "Donald Trump was my friend before the riot. And I'm trying to keep a relationship with him after the riot. I still consider him a friend. What happened was a dark day in American history, and we're going to move forward."

• "I want us to continue the policies that I think will make America strong. I believe the best way for the Republican Party to do that is with Trump, not without Trump."
• "Mitt Romney didn't do it. John McCain didn't do it. There's something about Trump. There's a dark side and there's some magic there."

Flashback: When Swan noted Trump is not showing remorse for his election challenge and still arguing he won in a landslide, Graham invoked McCain.

• "I tell (Trump) every day that he wants to listen that I think the main reason he probably lost in Arizona is beatin' on the dead guy called John McCain," the senator said.