When Stephen Colbert asked Joe Biden on Thursday whether he could patch up his once-close friendship with Sen. Lindsey O. Graham (R-S.C.), the president-elect’s expression turned somber.

Graham, a close ally of President Trump, has declined to acknowledge Biden’s election victory and was accused of pressuring Georgia to discard mail-in ballots in a state that went for the Democrat.

Biden, who has made his willingness to work with Republicans a key campaign promise, declined to say whether their relationship was salvageable.

“Lindsey’s been a personal disappointment because I was a personal friend of his,” Biden told the CBS host.

The late-night appearance comes as the president-elect faces the task of working with Senate Republicans who remain fiercely loyal to Trump in the last weeks of his term, which coincide with two crucial Senate runoff elections in Georgia for control of the chamber. Senate Majority Leader Mitch McConnell’s (R-Ky.) acknowledgment this week that Biden is the president-elect was met with derision from Trump and his allies, some of whom called for McConnell to retire, accusing him of giving up on the president.

Senate Majority Leader Mitch McConnell (R-Ky.) on Dec. 15 acknowledged Joe Biden as the president-elect from the Senate floor. (The Washington Post)

But Biden again expressed optimism on Colbert’s show that he could work with GOP leadership once Trump’s term ends next month.

“Once this president is no longer in office, I think you’re going to see his impact on the body politic fade, and a lot of these Republicans are going to feel they have much more room to run and cooperate,” Biden said.

The across-the-aisle bond that once existed between the president-elect and the South Carolina senator has been well-documented, with Graham once calling Biden “as good a man as God ever created.”

Despite their political differences, the pair traveled and dined together as members of the Senate Foreign Relations Committee, and Biden jokingly offered Graham his support in 2013 for reelection, saying he would “campaign for him or against him, whichever will help the most.” When Graham got emotional recounting a phone call he had with Biden following the death of his son Beau Biden in 2015, the senator concluded, “If you can’t admire Joe Biden as a person, then you got a problem.”

But the friendship fractured during Trump’s presidency as Graham became one of the closest allies of a president he originally disdained as a candidate. Then, Graham led the efforts to make Biden’s son Hunter Biden a focus of Trump’s impeachment proceedings, pushing for probes of the Biden family and Hunter’s business dealings in Ukraine.

Joe Biden soon lashed out at Graham, telling CNN last year that his former friend was “about to go down in a way that I think he’s going to regret his whole life.”

Just this week, Graham pushed for a special counsel to probe the business of Hunter Biden, who is under federal investigation. The president-elect again defended his son on Thursday, saying, “I’m not concerned about any accusations that have been made against him.”

While many Republican senators have finally recognized Biden as president-elect, Graham stopped short, maintaining that Trump still had a “very, very narrow path” after the U.S. Supreme Court dismissed a lawsuit to overturn the election results in four states Trump lost.

“I don’t see how it gets there from here, given what the Supreme Court did,” Graham said Monday. “But having said that, I think we’ll let those legal challenges play out.”

Graham’s spokespeople did not immediately return The Washington Post’s request for comment early Friday.

Colbert also asked the president-elect and Jill Biden, who joined him for the interview, to respond to a viral op-ed about the incoming first lady that many critics slammed as “misogynistic.”

A recent Wall Street Journal op-ed that addressed Jill Biden as “kiddo” and called for her to drop the honorific “Dr.” from her name because she’s not a medical doctor sparked swift backlash. The Journal later doubled down on the piece, blaming “cancel culture” for the attacks, and extending a rancorous debate, reported The Post’s Katie Shepherd and Kim Bellware. The dispute saw Fox News host Tucker Carlson repeatedly mock the future first lady’s honorific title this week.

Jill Biden called the op-ed “such a surprise” in the interview with Colbert.

“It was really the tone of it — he called me ‘kiddo,’ ” she said of the op-ed’s author, Joseph Epstein. “One of the things I’m most proud of is my doctorate. I worked so hard for it.” The community college professor earned her doctorate in education from the University of Delaware.