New Husseins began to crop up online as far back as last fall. But more joined up in February after a conservative radio host, Bill Cunningham, used Mr. Obama’s middle name three times and disparaged him while introducing Senator John McCain, the presumptive Republican nominee, at a campaign rally. (Mr. McCain repudiated Mr. Cunningham’s comments).

The practice has been proliferating ever since. In interviews, several Obama supporters said they dreamed up the idea on their own, with no input from the campaign and little knowledge that others shared their thought.

Some said they were inspired by movies, including “Spartacus,” the 1960 epic about a Roman slave whose peers protect him by calling out “I am Spartacus!” to Roman soldiers, and “In and Out,” a 1997 comedy about a gay high school teacher whose students protest his firing by proclaiming that they are all gay as well.

“It’s one of those things that just takes off, because everybody got it right away,” said Stephanie Miller, a left-leaning comedian who blurted out the idea one day during a broadcast of her syndicated radio talk show and repeated it on CNN.

Ms. Miller and her fellow new Husseins are embracing the traditionally Muslim name even as the Obama campaign shies away from Muslim associations. Campaign workers ushered two women in head scarves out of a camera’s range at a rally this month in Detroit. (The campaign has apologized.) Aides canceled a December appearance on behalf of Mr. Obama by Representative Keith Ellison, a Minnesota Democrat and the first Muslim congressman.

Mr. Obama may be more enthusiastic, judging from his response at a Chicago fund-raiser two weeks ago. When he saw that Richard Fizdale, a longtime contributor, wore “Hussein” on his name tag, Mr. Obama broke into a huge grin, Mr. Fizdale said.

“The theory was, we’re all Hussein,” Mr. Obama said to the crowd later, explaining Mr. Fizdale’s gesture.