Former Vice President Joe Biden threatened Sen. Lindsey Graham (R-SC) for launching an investigation into his activities with Ukraine while in the Obama White House, stating the Republican will “regret” the move his “whole life.”

On Thursday, Graham sent a letter to Secretary of State Mike Pompeo requesting documents to aid in determining whether Biden pushed for the firing of Ukrainian Prosecutor General Viktor Shokin to squash a sweeping probe into Burisma Holdings, the Ukrainian energy giant where his son, Hunter Biden, served as a board member. The younger Biden was compensated generously, making up to $83,000 a month for several years while on the Burisma’s board.

“Lindsey is about to go down in a way that I think he’s going to regret his whole life,” Biden told CNN host Don Lemon in a Friday interview in South Carolina. “I say Lindsey, I just — I’m just embarrassed by what you’re doing, for you. I mean, my Lord.”

Biden tells @donlemon he's "embarrassed by" Graham's actions after senator asks Pompeo to turn over docs related to Hunter and Ukraine "Lindsey is about to go down in a way that I think he’s going to regret his whole life," Biden says, adding Trump is "holding power" over him pic.twitter.com/sjNjQV7Ogp — Manu Raju (@mkraju) November 22, 2019

“They have him under their thumb right now. They know he knows that if he comes out against Trump, he’s got a real tough road for reelection, number one,” the former vice president continued about the South Carolina senator.

Biden then said he is “angered” by the probe because of his long friendship with Graham dating back to their time together in the Senate and suggested President Trump may have pressured him to launch the probe.

“He knows me; he knows my son; he knows there’s nothing to this,” he vented. “Trump is now essentially holding power over him that even the Ukrainians wouldn’t yield to. The Ukrainians would not yield to, quote, ‘investigate Biden’ — there’s nothing to investigate about Biden or his son.”

The senator requested all documents and communications related to Joe Biden’s phone calls with Poroshenko on Feb. 11, 18 and 19, and March 22, 2016, citing media reports that they discussed previous demands to dismiss Shokin for alleged corruption before he was removed from office on March 29, 2016.

Graham also requested documents and communications between Joe Biden and his office and Poroshenko and his office between Feb. 2, 2016, when Burisma founder Mykola Zlochevsky’s home was raided and Shokin’s dismissal.

Graham is also seeking all documents and communications related to a meeting between Devon Archer, a business partner of Hunter Biden, and then-Secretary of State John Kerry on March 2, 2016.

Graham’s request comes after two weeks of public testimony on the impeachment inquiry into President Donald Trump, which centers around a “whistleblower” complaint that Trump withheld military aid from Ukraine in an attempt to pressure newly elected Ukrainian President Volodymyr Zelensky to investigate Burisma and the Bidens.

The UPI contributed to this report.