The former president was campaigning in Summerville, South Carolina when he was forced to tamp down a sea of jeers after mentioning his "friend" Mr Graham.
"Another man who's always there, he's always — I tell you what, when I need help on the left, he's great, he's great. And he's my friend too — Lindsey Graham," Mr Trump said.
Boos immediately poured in from the crowd.
"Oh, no, no," Mr Trump said, literally handwaving the crowd's reaction.
But the boos did not stop.
"He helps me on the left. We need help sometimes. Republicans shouldn't need help on the left, but he helps me," Mr Trump continued through the jeers.
Mr Trump has made a bizarre habit out of referring to the staunchly Republican senator as a "progressive" — it was Mr Graham who first attempted to push for a national abortion ban following the fall of Roe V Wade — and insists he is integral in bringing Democrats to the table during votes.
It's unclear if there is one specific reason or a combination of reasons why Mr Graham's constituents seem to have turned on him.
The leading theory is that he has been inconsistent with his support of the former president.
Mr Graham opposed Donald Trump in 2016, first running against him in the Republican primaries and later saying he would not support the real-estate mogul as the nominee. The senator was featured in a campaign ad for Joe Biden in 2020 saying the current president is "as good a man as God ever created."
It's not exactly a popular line to take with MAGA supporters.
Mr Graham also backed away from Mr Trump following the Capitol riot, saying his time with Mr Trump had been a "journey" and that he hated it "has to end this way," but said "enough is enough." Despite his objection to the riot, he still refused to vote to impeach Mr Trump during his second impeachment.
He also admitted that Mr Trump may have "done things wrong" regarding the Mar-a-Lago classified documents scandal, but ultimately defended the former president, calling it a double standard that Hillary Clinton was not handled with similar scrutiny for her emails.
This isn't the first time Mr Graham has been booed in his home state. The Republican senator has been taking a lashing all summer long, especially when he appears at Trump events. Earlier this summer he was called a "traitor" by a crowd in South Carolina and had to leave a stage just six minutes into an event to help quell the boos, according to The Hill.
His response to his detractors?
"Thank you," he said to the booing crowd. "Thank you very much."