Interest groups are technically obeying an unusual effort to keep third-party advertising out of the Massachusetts U.S. Senate race — including one union that recently switched its Internet ads supporting Democrat Elizabeth Warren to ads supporting President Obama — but that hasn’t stopped them from finding other ways to try to sway the marquee matchup.
Super PACs and other groups have shelled out more than $2.3 million over the last two months for direct mail, phone banks and canvassing, efforts still allowed under a pact hammered out by Republican Sen. Scott P. Brown and Mrs. Warren that promised to donate to charity if any outside groups advertised on their behalf.
That amount is not much compared to other races around the country, where outside groups are spending millions of dollars on television, radio and internet ads. But it allows groups to honor the candidates’ agreement while still making their mark on one of the highest-profile — and most expensive — Senate races in the country.
Still, that’s not to say some groups haven’t come close to breaking the rules.
The United Food and Commercial Workers International Union bought nearly $15,000 in online ads last month for Mrs. Warren, according to Federal Election Commission filings. But once officials learned the ads weren’t allowed under the ban, they revamped them to support Mr. Obama instead, said union spokesman Tim Schlittner.
“We’re strong supporters of Elizabeth Warren and if this is the pact she agreed to, we don’t want to violate that,” Mr. Schlittner told The Washington Times. “We’re here to help, not to harm.”
The ban covers both positive and negative ads and even prevents the party committees (both the Republican and Democratic National Committees and the National Republican Senatorial Committee and the Democratic National Senatorial Committee) from spending independently in the race.
And after a handful of infringements last spring forced Mr. Brown to donate about $35,000 to charity, both campaigns agreed to make the ban stricter, adding issue-specific advertising to the list.
But the major PACs and super PACs on both sides have still found plenty of ways to try to influence the race.
Americans for Tax Reform and a super PAC called America 360 have spent a combined $718,397 on mailers opposing Mrs. Warren, while Karl Rove’s Crossroads GPS has paid $230,000, chiefly on phone calls and direct mail. Women Vote!, a super PAC affiliated with the pro-choice group Emily’s List, has spent $261,156 on mailings opposing Mr. Brown.
Other groups have spent money in more creative ways. The International Brotherhood of Teamsters reported spending $1,745 on a banner for Mrs. Warren, a Harvard professor, while a firefighters union rented a motor coach, wrapped it in a pro-Warren message and drove it around Springfield, Mass., where the two candidates debated last week.
With interest groups champing at the bit to get involved, it’s questionable whether the advertising ban will hold all the way to Election Day. And they’d be well within their rights to ignore the candidates’ wishes and buy advertisements anyway, since campaigns are legally prohibited from directly coordinating with them.
Political analysts say that will become more likely if the race remains close, possibly prompting some groups to launch a last-minute ad blitz in hopes of swaying the election. Recent polls have shown Mr. Brown trailing anywhere from two to six points after holding a slight lead until last month.
“The problem with these voluntary agreements is that you can’t close every single loophole,” said Rob Gray, a Boston-based Republican political strategist. “Super PACs on the left and right have certainly driven a car through the loophole by buying mail and paid phone calls, and they may well drive a truck through it by Election Day and increase those efforts.”
Some groups are upfront about their efforts to find loopholes. Launching a broad grass-roots campaign to propel the race in Mrs. Warren’s favor, the League of Conservation Voters has dolled out nearly $1 million for telemarketing calls, canvassing and mailings.
“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.”