(CNN) - A Democratic candidate in Massachusetts who hoped to challenge Republican Sen. Scott Brown in next year's election is calling it quits.
Alan Khazei is expected Thursday to withdraw from the race, a Democratic source confirms to CNN. Earlier in the cycle, the social entrepreneur and "City Year" co-founder was one of the top contenders for the Democratic Senate nomination, but after the late summer entry into the race by Harvard University law professor and consumer advocate Elizabeth Warren, Khazei has had a hard time keeping pace.
Warren, whose Senate bid enjoys the strong backing of a number of leading national progressive groups, was named a special adviser by President Barack Obama to oversee the development of the newly created Consumer Financial Protection Bureau. This year she was in contention for –but was not nominated as - the director of the new bureau. She left Washington in early August and returned to Massachusetts, a move that stirred rumors she would launch a bid for the Senate. She set up an exploratory committee in mid-August and formally entered the race last month.
Warren raised $3.15 million in campaign fundraising in the last month and a half of the third quarter. Brown brought in $1.55 million in the July through September period, with more than $10 million in the bank.
Warren joined a crowded field of candidates bidding for their party's Senate nomination when she announced, but none of the other contenders, including Khazei, had strong name recognition across the Bay State. Some national Democrats were concerned that the other candidates would not be able to effectively challenge Brown, who made national headlines by beating Democratic state Attorney General Martha Coakley in a special election early last year to replace the late Democratic Sen. Ted Kennedy, who held the seat for nearly five decades.
While the most recent polls indicate Brown remains popular in Massachusetts, the surveys also indicate Warren is competitive with the senator in hypothetical 2012 general election matchups.
– Follow Paul Steinhauser on Twitter: @PSteinhauserCNN.