Few can match Brown's gripping biography, from his upbringing amid alcoholism, poverty and domestic violence, to his education at Tufts and Boston College law school, to his careers in modeling, the military and politics. Yet Warren, a native of Oklahoma, also has a compelling tale that she often telescopes into a few vivid sentences. After her father had a heart attack, she says, her family existed on "the ragged edge" of the middle class. "We lost our car. We almost lost a house," she told one man at The Student Prince. She later told reporters that she was babysitting by age 9, waiting tables at 13, married at 19, a mother and elementary school teacher at 22.

As for Republicans who dismiss her as a liberal academic, "I grew up hanging on to the edge of the middle class by my fingernails," Warren said. "All I can say is I've been there. I've lived this. My family lived one pink slip, one bad diagnosis away from falling off the economic cliff. Yeah, I've got a fancy job at Harvard and I've gotta tell you, I'm proud of that job. I worked hard to get there. I wasn't born at Harvard. I was born to a family that had to work for everything it's got."

Brown cultivated independents and a moderate image en route to his stunning victory in the special election for Ted Kennedy's seat early last year. His voting record is a pastiche that offers ammunition for both parties. On the conservative side of the ledger, he opposed the DREAM Act and the Affordable Care Act and voted against Supreme Court nominee Elena Kagan and Craig Becker, named to the National Labor Relations Board. On the other hand, he voted against GOP Rep. Paul Ryan's controversial budget cuts, for the Dodd-Frank Wall Street regulation law and for the repeal of the military's don't ask, don't tell policy on gay troops.

Warren is by far the biggest name in the Democratic primary and is already pulling in national money from Democrats determined to oust Brown. By midday Thursday, she was the "busiest recipient" at the ActBlue.com fundraising clearinghouse, with more than $310,000 in contributions. EMILY's List sent out a fundraising email on her behalf headlined "It's on in Massachusetts," asking members to "stop Scott Brown and the Tea Party in their tracks."

In addition to liberals and women, Warren can expect strong support from labor. She energized a union audience on Labor Day in a populist speech that included a mention of her brother, a retired crane operator who was a union member. She also has close ties to small business. Her daughter runs one, she told a voter, and wants a simpler tax code. She knows there are loopholes that might help her, Warren said, but she can't afford to hire a lawyer to find them.

While Warren is a heroine in some circles for conceiving, pushing and setting up a Consumer Financial Protection Bureau that passed last year in a Wall Street reform bill, it's unclear how much Massachusetts voters know about her. Six men walking into The Student Prince during her visit said they were there for dinner, not Warren. "Who's she?" one of them asked.