On Sunday, Senator Kelly Loeffler, a Republican in one of the runoff elections in Georgia next month, fielded questions and sparred with her Democratic opponent, the Rev. Raphael Warnock, in a televised debate.

But on the internet, some Democrats saw evidence of foul play — a light-colored strand on Ms. Loeffler’s head that they claimed, without evidence, proved that she was being fed answers onstage.

Ms. Loeffler was not wearing a wire, and the mysterious filament was likely just a strand of hair that caught the light. The Atlanta Press Club, which hosted the debate, tweeted on Monday that Ms. Loeffler and Mr. Warnock “had no audio assistance from their campaigns.” A spokesman for Ms. Loeffler’s campaign sent a link to the Atlanta Press Club’s tweet debunking the rumor when asked for comment.

The claim has not been shared by many prominent Democrats. But it was shared by some liberals on Twitter, including Ben Meiselas, a lawyer with 100,000 followers who has previously shared other baseless theories, including suggesting that Ms. Loeffler might be “Q,” the central figure in QAnon.

Conspiracy theories about politicians wearing hidden wires and earpieces during debates are decades old. They date to the 2000 presidential election, when the right-wing talk radio host Rush Limbaugh advanced the false theory that Al Gore had gotten hidden help from his campaign during a debate with George W. Bush.

In the two decades since, Democrats and Republicans have advanced similar theories. This year, some Republicans speculated, falsely, that Joseph R. Biden Jr. was receiving assistance through an earpiece, a claim that was quickly debunked.