The battle over the seat once held by Sen. Edward Kennedy (D) remains tight, with the Democratic challenger garnering 48 percent support versus 44 percent for Senator Brown, in a new Suffolk University poll of statewide voters.
That gap is just at the poll's margin of error, of plus or minus 4 percentage points, but it comes after other surveys this month have shown Ms. Warren leading, in one case by 2 percentage points and in another by 6 percentage points.
Brown – whose victory in a 2010 special election stunned Democrats – has the advantage of being an incumbent, but the disadvantage of being a Republican in a strongly Democratic state.
Ms. Warren may have gained some ground from the Democratic National Convention, where voters could see her giving a prominent speech and inhabiting the same televised space as Bill Clinton and President Obama. Brown, meanwhile, may have lost ground not because of personal missteps but because of wider challenges for his party.
In a May Suffolk University poll, for instance, 59 percent of Massachusetts voters said they would vote to reelect Obama, while 39 percent said they would opt for Republican Mitt Romney or were undecided. In the new poll, taken Sept. 13 to 16, Obama's share has risen to 64 percent and Romney's support has shrunk correspondingly.
Back in May, Warren and Brown were essentially tied. Even now, the race continues to be very tight.
Perhaps the most notable shift since May is a rise in the favorability rating of Warren, a Harvard University law professor who has won national recognition as a pro-consumer voice, opposed to big Wall Street banks. The share of Bay State voters viewing her favorably has risen from 43 percent to 52 percent.
That, coupled with voters perception that she's the candidate most likely to stand up for the middle class – a central pitch made by both campaigns – makes her a formidable opponent for Brown.
The poll also showed a decline in the share of voters concerned whether Warren benefited in her academic career by listing herself as a minority, based on a thread of Cherokee ancestry she has claimed to have. More than half of Massachusetts voters don't think she has used that claim to gain an advantage over academic rivals.
Despite these factors now tilting in Warren's direction, Brown is staying competitive because he is popular and perceived as an independent advocate for his constituents. His favorability rating has risen since May from 58 percent to 60 percent, and a number of Democratic politicians in the state have endorsed him.
Warren's efforts to cast a negative light on his ties Wall Street have so far failed to stick.
The Suffolk poll also found voters saying that Brown is the more independent of the two, and is running the better campaign.
Both candidates are vying for a hotly contested pool of undecided women, with Warren seeking the high ground as a stronger advocate of abortion rights. Still, the Suffolk poll found 78 percent saying they don't think Brown is anti-women. Warren's gains in support since May have come from both men and women.
Although both candidates are seeking to play up their opponent's negatives, voters generally say they're making choices for positive reasons. About 85 percent say their vote will be "for" one candidate, rather than "against" the other.