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“We’re prohibited from running ads because of the agreement by the candidates, so we’re running a massive door-to-door operation,” vice president Mike Palamuso told The Times.

But even that effort may not have a huge effect on the race, considering the massive sums of money being raised and spent by both candidates. They’ve raised a combined $63.8 million in the race so far, putting them about $5 million away from becoming the most expensive Senate race in history. Right now, that title belongs to Hillary Rodham Clinton and former Rep. Rick Lazio in their 2000 New York Senate race.

The airways are already flooded with ads by the campaigns themselves, leaving little room for outside groups to carve out a niche, said Brian Frederick, a political science professor at Bridgewater State University.

“If [outside groups] get involved in either side, it’s not going to have much of an impact,” Mr. Frederick said. “As a normal viewer, it would be virtually impossible to see any more ads in the Massachusetts Senate race. When you turn on the TV, literally every other ad is a campaign ad for one of the candidates.”