Sen. Lindsey Graham (R-S.C.) leveled a serious charge against his colleague Sen. Harry Reid (D-Nev.) on Sunday, accusing the Senate majority leader of lying on the Senate floor when he said he’d heard Mitt Romney didn’t pay taxes for a decade.

“I’ve been around this town for a while,” Graham told Candy Crowley on CNN’s "State of the Union." “I actually like Harry. But what he did on the Senate floor is so out of bounds. I think he’s lying about it.”

Reid recently told The Huffington Post in an interview that he’d heard from an early Bain Capital investor that the presumptive GOP presidential nominee didn’t pay taxes for 10 years; he then reiterated the charge on the Senate floor later in the week, prolonging a drama that consumed much of the political news cycle.

“So, the word’s out that he hasn’t paid any taxes for 10 years. Let him prove that he has paid taxes, because he hasn’t,” Reid said on the floor. “We already know from one partial tax return that he gave us, he has money hidden in Bermuda, the Cayman Islands and a Swiss banking account."

The accusation, from which Reid has not backed down, infuriated the Romney campaign, putting the former Massachusetts governor in the awkward position of having to release more taxes if he wants to debunk Reid’s charges. Romney has insisted he’s paid taxes every year, although he hasn’t said just how much.

“I have paid taxes every year,” Romney insisted. “A lot of taxes.”

In his interview with The Huffington Post, Reid clarified that he didn’t know if it was true Romney hadn’t actually paid any taxes.

"He didn't pay taxes for 10 years! Now, do I know that that's true? Well, I'm not certain," Reid said. "But obviously he can't release those tax returns. How would it look?"

"I just cant let that pass," Graham told Crowley. "I can't believe the majority leader of the United States Senate would ... make accusations that are unfounded in my view."