But there is much chatter in the state about the pact being broken before Election Day and Spencer, Cignoli and others say the common question is whether Brown supporters will be the ones to thwart it.
"The feeling is it's inevitable it will be broken," Cignoli said.
But while Spencer says that he hears the pledge's end frequently discussed in political circles, he doesn't subscribe to the theories. "Brown initiated this. If [outside spending on the] right comes in, he's going to look bad... like just another phony politician," Spencer said.
Another note: Brown supporters have already broken the pledge twice.
Brown's campaign paid $1,000 to the Autism Consortium in March after a group called CAPE PAC purchased Google ads in support of Brown. Later that month, Brown agreed to donate over $34,000 to charity after the American Petroleum Institute ran radio and print ads urging voters to tell Brown to oppose a tax hike on energy companies-- a position he had already taken. At the time, issue-specific advertising was not covered by the agreement. But Brown agreed to close the loophole.
Brown's team said they are hopeful the pact will remain in place through Election Day.
"We're pleased that Scott Brown's People's Pledge has kept outside groups and super PACs off the Massachusetts airwaves, and we're hopeful the special interests on both sides will remain out of our race through the election," Brown communications director Colin Reed wrote in an email to Yahoo News. "This race will be decided by the people of Massachusetts based on the very real differences between Scott Brown's independent leadership and pro-jobs agenda, and Elizabeth Warren's job-destroying tax and spend philosophy."
Warren's camp also expressed support for the ban, but expressed no doubt about the ban's longevity. "Elizabeth believes the people of Massachusetts are entitled to hear from the candidates themselves--in their own voice--their best case for why they should be in the United States Senate. And for months now that's been the case here in Massachusetts," Warren press secretary Alethea Harney wrote in an email to Yahoo News. "That's how Elizabeth believes elections ought to work and she expects that the pledge will continue through Election Day."
Republicans groups say if it weren't for the pact they'd be involved in the race, but they intend to respect the agreement.
Jonathan Collegio, a spokesman for American Crossroads, pointed out that they have remained quiet in 2012 "to this point."
"Crossroads will be engaged in a variety of Senate contests and as our previous advertising shows, Massachusetts would have been one of those states," Collegio said.
Independent polls stretching back to March show the race tied or nearly in a dead heat with 15 percent or fewer of voters still undecided.
With such a small segment of undecided voters and no outside help available, strategists say debates between Brown and Warren scheduled for this fall have gained new importance.
Brown and Warren late last month agreed to meet for four televised debates between now and Election Day.
"The media usually puts much more stock in debates than they're worth," Spencer said. "But in this particular campaign, these debates are huge."