In 1994, Gingrich became the subject of a lengthy ethics investigation, and although he wasn't found guilty on any of the 84 charges it resulted in a reprimand from the House Ethics Committee, a $300,000 penalty, a decrease in support from the GOP caucus and his eventual departure from Congress.
Those ethics charges have become fertile territory for front-runner Romney and the super political action committee that backs him.
The super PAC bombarded voters in Florida and Nevada with ads replaying news feeds from that time -- and contributed to Romney's success in the two states' presidential preference selection process, analysts said.
"There's no question that those ads have had a devastating effect on Gingrich," Dan Schnur, a California political analyst, told The Atlanta Journal Constitution in an interview published Monday.
"Not surprisingly, the Romney campaign and his outside allies are going to continue to attack on this front," Schnur said.
"'Innocent on all charges' is a legitimate defense," he said, "but it's not much of a bumper sticker. Even though he's got a good answer, he's still talking about what Romney wants him to be talking about."
"They didn't find him guilty of a durn thing," said Mel Steely, Gingrich biographer and a former staff member, who denounced what he calls Romney's misleading ads. "You can't turn the TV on without this terrible onslaught against Gingrich. It's just unrelenting."