U.S. Sen. Scott Brown and his chief Democratic rival Elizabeth Warren have both signed a pledge to curb political attack ads by outside groups.
Warren on Monday sent a letter to Republican incumbent Brown urging him join her and sign an agreement to prevent third-party ads. Brown, who had initially proposed the pledge, signed the deal minutes later.
Top level staffers for both candidates failed to reach a deal during a meeting last week.
Warren in her letter said "we don't want outsiders running this election" and said her agreement sews up loopholes in a proposal Brown made last week.
Brown suggested that each candidate donate half the cost of any third-party ad to charity if that ad either supports their candidacy or attacks their opponent.
Warren says it's a historic agreement to try and curb third-party influence.
"If we do this it will be the first time that any two campaigns have gotten together like this and tried to hold out third-party groups," she said.
Brown, in a statement, called the agreement a "great victory for the people of Massachusetts."
With reporting by The Associated Press and the WBUR Newsroom
This article was originally published on January 23, 2012.
This program aired on January 23, 2012. The audio for this program is not available.