The race between Massachusetts Senate race between Republican Senator Scott Brown and Elizabeth Warren, his Democratic challenger, took an aggressive turn Thursday night, when the candidates faced off in the first of four debates before Election Day.

Brown, who has trailed Warren in a handful of recent polls, kicked off the night on a personal note, demanding that Warren release her personnel records from Harvard University Law School to prove that her Native American heritage did not play a role in her hiring.

“You refuse to release your records, and I think that speaks volumes,” he said.

Warren's heritage has become a thorny issue for the Harvard bankruptcy professor for several months, after a report from the Boston Herald found that she listed herself as a Native American on law school directories during the 1990s. Although Warren insists that she did not benefit academically or professionally from the listing, she has continued to be tripped up by the story as subsequent reports have questioned whether she is, in fact, part Native American.

"My mother was part Delaware and part Cherokee," Warren said tonight. “There’s nothing else there. The question has been asked and answered. I think the senator just doesn’t like the answer."

"I was going to start by saying Senator Brown is a nice guy," she added.

"First of all, you're a nice woman, too," Brown replied. "But this is about character."

What followed was an hour of rapid-fire back-and-forth between the candidates, who are competing in one of the most closely-watched and expensive Senate races in the country this year.

Referring to Warren almost exclusively as "Professor," Brown focused his attacks on Warren's ideology, at one point even labeling her "the founder of the radical Occupy protest movement."

"She's obsessed with raising taxes," he said early on, spelling out an argument he repeated several times throughout the debate.

But Warren kept her cool, systematically going through Brown's voting record to cast him as a conservative party-line Republican whose policies are bad for women and the middle class. In the end, she closed the debate by laying out the stakes of the race, emphasizing to Democratic-leaning Massachusetts voters that a vote for Brown could hand control of the Senate to Republicans.

"I’m still working to have Obama be commander-in-chief," she said. "Not Mitt Romney."