Former Vice President Joe Biden ripped into Sen. Lindsey Graham (R-SC) Friday after the senator requested documents on Biden, Graham’s old friend, to pursue a pet conspiracy theory of President Donald Trump’s.

Graham on Thursday requested materials from the State Department related to Biden and Burisma, the natural gas company that employed Biden’s son Hunter on its board.

“They have him under their thumb right now,” Biden told CNN’s Don Lemon, referring to Graham. “They know he knows if he comes out against Trump he’s got a real tough road for re-election.”

Biden and Graham go back decades. After the death of Biden’s son Beau in 2015, Graham recorded a tearful interview in which he called Biden “the nicest person I think I’ve ever met in politics” and “as good a man as God ever created.”

Biden alluded to that in the interview Friday.

“I am disappointed, and quite frankly I’m angered by the fact — he knows me,” Biden said. “He knows my son. He knows there’s nothing to this.”

Biden compared Graham to the Ukrainians, who didn’t acquiesce to the pressure campaign from the White House to pursue a politicized investigation into Burisma and other matters. Trump pushed Ukraine to investigate whether Biden wanted the country’s then-top prosecutor fired order to protect Hunter from investigation, a widely debunked claim.

“Trump is now essentially holding power over him that even the Ukrainians wouldn’t yield to,” Biden said. “The Ukrainians would not yield to, quote, ‘investigate Biden.’ There’s nothing to investigate about Biden or his son.”

“Lindsey is about to go down in a way that I think he’s going to regret his whole life,” he added.

Asked what he would tell Graham, Biden responded bluntly, “I say Lindsey, I’m just embarrassed by what you’re doing, for you. I mean, my lord.”