Rep. Niki Tsongas is endorsing Harvard law professor Elizabeth Warren, a Democrat running against incumbent GOP U.S. Sen. Scott Brown.
A member of Warren's campaign told the Associated Press on condition of anonymity that Tsongas will endorse Warren in Lowell Monday afternoon. The source requested anonymity because the announcement had not yet been made.
Tsongas is the first major Democratic political figure to endorse Warren, who jumped into the race last month.
Tsongas is the only woman in Massachusetts' congressional delegation.
The endorsement comes one day after a new UMass Lowell-Boston Herald poll of more than 1,000 registered voters gave Warren 38 percent of the vote to Brown's 41 percent, within the poll's margin of error.
The six Democratic Senate candidates face off in their first debate Tuesday.
This program aired on October 3, 2011. The audio for this program is not available.