"Could I see your green card?" Burns asks in the video. "And Hugo says: 'No.' I said: 'Oh, gosh.'"

The Burns campaign maintains the man is not an illegal immigrant and that the comments weren't mean-spirited, but for the senator, in a tough re-election fight this year, his loose-tongued history could soon become a serious liability, political observers say. Add to the recent gaffes a speech about energy seven years ago in which he called Arabs "ragheads." He apologized for that comment, too, and was re-elected to the Senate the following year. "Individually, these inappropriate comments didn't hurt," says Jennifer Duffy, a political analyst with the Cook Political Report. "But the volume has created the sense that maybe he's embarrassing us."

Burns himself acknowledges that he has an uncanny knack for putting his foot in his mouth. "I can self-destruct in one sentence," he told reporters a few months ago. "Sometimes in one word."