“The people of Massachusetts should hear directly from the candidates, not from a bunch of shady outside groups that have their own agendas,” Warren said in an interview with the Globe.

Warren wants a reprise of the “people’s pledge’’ she and then-Republican Senator Scott Brown agreed to in 2012.

WASHINGTON — Elizabeth Warren doesn’t have an opponent yet in her 2018 re-election bid, but she already has a proposal: Join her in a pledge to keep third-party political groups from dumping buckets of cash into the race.

The groundbreaking pact signed by Warren and Brown required the candidates to notify outside groups that they didn’t want them to advertise on their behalf on television, radio, or the Internet. If an outside group ran an ad anyway, the candidate who benefited from the ad pledged to donate half the value of the ad to a charity chosen by his or her opponent — which Brown did twice.

Warren’s early demand could become a factor for any Republican pondering a challenge of the liberal senator, who is a national figure with a giant online fundraising list. Several potential challengers are testing the waters, including major GOP donor and businessman John Kingston and state Representative Geoff Diehl, who was a leader in Trump’s Massachusetts campaign.


Diehl said in an interview that he wouldn’t be inclined to sign the pledge if he decides to get into the race. “This proves what a hypocrite she is. She wants to rig the system” with her head-start in fund-raising, he said. Warren has $4.8 million cash on hand in her campaign account, according to the Center for Responsive Politics, a non-profit that tracks money in politics.

The Massachusetts Republican Party “will leave it to individual candidates to determine the best strategies for their own campaigns,” said spokesman Terry MacCormack.


“Senator Warren is clearly struggling to regain credibility on the issue of campaign finance given her track record of accepting donations from the very financial entities she rails against,” MacCormack said. He pointed to news reports that Warren has received hundreds of thousands of dollars in campaign donations from people who work at firms in the financial world, which she made her name criticizing. He also noted she accepted donations from so-called corporate political action committees, or PACs, once she was sworn in.

Warren said she would only make the commitment to shun outside advertising if her opponent agrees as well. “It takes both candidates to make The People’s Pledge work,” she said.

A 2013 analysis by Massachusetts Common Cause, a group that advocates for campaign finance reform, concluded that despite the Warren-Brown contest being the most expensive congressional race of 2012, the pledge drastically reduced outside spending compared to other expensive races that year. The analysis found that it slashed the relative influence of wealthy donors to the benefit of small-dollar donors, and also led to far less negative advertising overall.

Nonetheless, there were those who argued at the end of the 2012 race that the absence of outside group advertising actually contributed to the nasty tenor of the campaign, as the candidates were forced to sling mud at one another directly. “The Ugliest Campaign in America,” concluded BuzzFeed.

“Fair enough. It was a hard fought campaign,” said Warren. But she pointed back to reports that found the total number of negative ads in her 2012 race was sharply lower than elsewhere in the country where outside groups dominated.


She said she hopes this next race is not as nasty.

“I wish the system were different. I wish that we could take steps across the country to get money out of politics but the People’s Pledge is a step I the right direction. It doesn’t fix everything, but it will make our race in Massachusetts better.”

Victoria McGrane can be reached at victoria.mcgrane@globe.com. Follow her on Twitter @vgmac.