(CNN) - A new poll indicates Democratic Senate hopeful Elizabeth Warren of Massachusetts is holding on to her narrow margin over incumbent Sen. Scott Brown in the Massachusetts Senate race, but nearly a fifth of voters say they're still undecided.
Forty-three percent of likely voters back Warren, while 38% support Brown, according to the Boston Globe poll released Sunday.
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The five-point difference, however, falls within the survey's sampling error, meaning the two candidates are statistically tied. The new poll marks the latest in a string of surveys putting Warren ahead of Brown since the Democratic National Convention, where Warren delivered a high-profile speech.
However, a University of Massachusetts/Boston Herald survey last week indicated Brown was up by four points.
While Brown has high marks in likability and job performance, many voters say they will vote with their political party, which could hurt Brown in the typically blue state. Democrats outnumber Republicans by a margin of 3-to-1 in Massachusetts.
Eighteen percent, though, say they haven't made up their minds for the November election.
Sunday's poll was conducted after the duo's first debate on September 20, when the opponents exchanged pointed barbs over their respective characters and records. Brown especially attacked Warren over a scandal involving her heritage. His campaign has consistently hammered Warren for listing herself in faculty directories as having Native American roots while teaching Harvard University.
Warren fought back on the attacks, saying she learned from her family she was "part Delaware and part Cherokee" and arguing she has never used her heritage to advance her career.
But the incumbent senator continued to push the offensive last week, releasing two television ad criticizing Warren over the issue. Warren herself released an ad responding to the criticism.
"Let me be clear. I never asked for or never got any benefit because of my heritage," she says in the spot. "The people who hired me have all said they didn't even know about it."
While the new poll shows that the story has become widespread in the state - 79% of voters are either very or somewhat familiar with the issue - the controversy seems to be having little impact. Seventy-one percent say the story has no influence on their ballot choice, according to the Globe poll.
The two face again in their second debate Monday night.
For the survey, 502 likely voters were interviewed by telephone between September 21 and September 27. The sampling error is plus or minus 4.4 percentage points.