He told Biden to “pass the torch.” It cost him his role in a state campaign.

Clint Keaveny took a seat in the bleachers behind President Biden at a rally in Madison, Wisconsin, on Friday and held up a sign that read, “Pass the torch, Joe.” Before the rally was over, Keaveny had lost his role in the Democratic congressional campaign.

The event was the first in Mr. Biden’s weekend blitz of campaign events in must-win states designed to deflect critics after his stuttering June 27 debate performance. As the president took the stage, in full view of cameras, Mr. Keaveny unveiled his poster, made of printer paper taped together and tucked into his waistband. It had been written by Mr. Keaveny’s mother, he said.

The moment quickly went viral. His boss noticed.

Before Mr. Keaveny even left the event, Kristin Lyerly, the congressional candidate from Wisconsin for whom he was a communications volunteer, had seen the footage circulated online. She called him and asked him to step down from the campaign, which he agreed to.

“He held up a sign that was not consistent with the values ​​and ideals of our campaign,” Dr. Lyerly said in an interview. “I was so disappointed that I called him right away.”

Keaveny, 27, said Biden has been a great president, but he doesn’t believe he can beat former President Donald J. Trump in November.

“It pains me to feel like a black sheep,” Mr. Keaveny said. “But I believe in following my conscience.”

The episode with Mr. Keaveny comes as questions about loyalty to President Biden are emerging in the Democratic Party and some are calling for a new nominee. Mr. Biden has repeatedly promised to stay the course.

Dr. Lyerly is running for a vacant seat that represents much of northeastern Wisconsin, including Green Bay, a competitive, Republican-leaning district. Rep. Mike Gallagher, a Republican, resigned from the seat in April.