DAVID GREENE, HOST:
And let's turn now to the Senate race in Massachusetts, where something rare in politics is happening: Rivals have joined forces. Senator Scott Brown, a Republican, and his Democratic challenger Elizabeth Warren have signed a pledge to try to block third-party political advertising.
The two sides negotiated for about a week to reach the deal, which has financial penalties if it's broken. It appears to be the first time opposing candidates have come together to stop the aggressive ad campaigns encouraged by the Supreme Court's Citizens United decision. From member station WBUR in Boston, Monica Brady-Myerov has our story.
MONICA BRADY-MYEROV, BYLINE: Brown and Warren wanted to make this more than a political pinky swear. So the deal requires each candidate donate to charity half the cost of any outside ad that either supports a candidate or attacks his or her opponent. Here's Harvard Professor Warren.
ELIZABETH WARREN: We're saying that we want to be able to run our own campaigns. You know, for me, this is a matter of personal responsibility. I will be responsible for what I say, and I assume that Scott Brown is willing to be responsible for what he says.
BRADY-MYEROV: The agreement covers broadcast and cable television, radio and Internet ads. Senator Brown, who first proposed the idea, says the pledge is a bold statement to superPACs that their influence in the race could hurt the candidates they're trying to help - hurt them with ads like this one.
(SOUNDBITE OF POLITICAL ADVERTISEMENT)
BRADY-MYEROV: That ad campaign by the League of Conservation Voters cost $1.8 million. Now, under Brown and Warren's People's Pledge, if the League makes a similar ad buy, Warren's campaign would be required to donate $900,000 to a charity of Brown's choice. The League's Navin Nayak says his organization will respect the agreement, howeverâ¦
NAVIN NAYAK: Our biggest concern is we hope that Senator Brown will actually hold up his end of the bargain when we inevitably see Crossroads and the Koch brothers break it.
BRADY-MYEROV: Crossroads GPS is an outside money group co-founded by Karl Rove that has run ads in Massachusetts attacking Warren.
(SOUNDBITE OF POLITICAL ADVERTISEMENT)
BRADY-MYEROV: The head of Crossroads says the agreement has loopholes the Teamsters could drive a truck through. It still allows outside groups to pay for union phone banks, direct mail and get-out-the-vote drives. How the pledge plays out will be closely watched, says Tufts University Political Science Professor Jeff Berry.
JEFF BERRY: If it does, in fact, work, then pressure will grow in the next election cycle for candidates to agree to this kind of truce.
BRADY-MYEROV: The candidates have also asked broadcast stations to refuse to run political ads produced by third parties. So far, no Boston station has agreed to comply with the pledge.
For NPR News, I'm Monica Brady-Myerov in Boston.