Republican Sen. Lindsey Graham on Monday doubled down on his calls for former Vice President Joe Biden’s son, Hunter, to be investigated by Congress, signaling he is not moved by his friend and former Senate colleague's bitter allegations that the South Carolina lawmaker is being controlled by President Trump.

BIDEN FUMES AT GRAHAM OVER REQUEST FOR DOCUMENTS ON SON

“I love Joe Biden as a person but we are not going to give a pass to what is obviously a conflict of interest,” Graham said in a Monday morning tweet. “I believe Hunter Biden’s association on the Burisma board doesn’t pass the smell test. If a Republican was in the same position, they’d certainly be investigated!”

The tweet appeared to be in response to comments made during a recent interview with CNN’s Don Lemon. During that interview, Biden said he was “disappointed and quite frankly … angered” because Graham “knows me, he knows my son, he knows there’s nothing to this.” Biden claimed Graham was acting out of fear of opposing Trump and risking reelection.

"Trump is now essentially holding power over him that even the Ukrainians wouldn’t yield to," Biden said, later adding, "I’m just embarrassed by what you’re doing, for you. I mean, my Lord!”

Graham had sent a letter to Secretary of State Mike Pompeo Thursday asking for documents related to contacts between both Bidens and former Ukrainian President Petro Poroshenko.

Specifically, Graham asked for documents and transcripts of conversations from 2016 between then-Vice President Biden and Poroshenko in relation to an investigation into Ukrainian natural gas company Burisma Holdings, where Hunter Biden had served as a board member. It is Trump's request for Ukraine to investigate the Bidens that has led to the ongoing impeachment inquiry against the president.

In his CNN interview, Biden claimed that his personal relationship with Graham should provide a basis for the senator not to go down that road.

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Speaking on Fox News’ “Hannity” on Wednesday night, Graham said the phone calls between Biden and Poroshenko coincided with the time frame in which Ukrainian prosecutor Viktor Shokin was fired. Shokin was investigating Burisma Holdings at a time when Hunter Biden sat on its board and while the vice president was leading the Obama administration's diplomatic dealings with Kiev. Though the timing raised concerns among anti-corruption advocates, many Western nations had supported Shokin’s firing.

House Intelligence Committee ranking member Rep. Devin Nunes, R-Calif., along with Rep. Jim Jordan, R-Ohio, notified Intelligence Committee Chairman Rep. Adam Schiff, D-Calif., that they plan on subpoenaing Hunter Biden for a closed-door deposition.

Fox News' Andrew O'Reilly and Charles Creitz contributed to this report.