The 2012 senatorial election in Massachusetts is starting to heat up. Republican Senator Scott Brown is under attack from critics accusing him of sexism for his response to a quip by one of his Democratic challengers, Elizabeth Warren.

During a debate on Tuesday night, the six Democrats vying for their party’s nomination in November’s election were asked how they paid for their college educations; the moderator noted that Brown posed nude in a Cosmopolitan photo spread to help finance his education at Boston College Law School.

Warren answered “I kept my clothes on,” in a thinly veiled shot at Brown, before going on to explain that she paid for college by taking out student loans and held a part time job.

On Thursday, when asked about Warren’s remarks on a Boston radio show, Senator Brown laughed and said, “Thank God.”

Although Warren took Brown’s shot in stride, remarking that “I’ll survive a few jabs from Scott Brown over my appearance,” other Massachusetts Democrats are up in arms over Brown’s comment.

“Scott Brown’s comments send a terrible message that even accomplished women who are held in the highest esteem can be laughingly dismissed based on their looks,” said Clare Kelly, the executive director of the Massachusetts Democratic Party. She went on to label Brown’s comment as “kind of thing you would expect to hear in a frat house, not a race for U.S. Senate.”

The controversy over Brown’s remarks promises to be just the first of many flare-ups in the highly publicized election. Brown has been very closely scrutinized after pulling off a shocking upset victory in the January 2010 special election to fill Ted Kennedy’s seat. Despite upsetting some conservatives with his occasional willingness to cross party lines, Brown is popular in Massachusetts, with his approval rating consistently polling above 50 percent.

Warren, his likely opponent, is also highly regarded. Just as Brown’s upset victory made him a hero to many Republicans, Warren’s work to develop the Consumer Financial Protection Bureau has earned her a devoted progressive following. The time is right for Warren to make a big move politically: She is known for the kind of fiery anti-Wall Street rhetoric that is stealing headlines across the country by way of the Occupy Wall Street movement. Indeed, Warren seems determined to frame the election as a choice between a Republican who will fight for Wall Street and a Democrat who will fight for the people.

“Forbes magazine named Scott Brown Wall Street’s favorite senator. I was thinking that’s probably not an award I’m going to get,” Warren said on Wednesday.

Warren and Brown’s back-and-forth over nude modeling served as the opening shot in what promises to be a bitter fight. It may be a must-win for Democrats; with the GOP in good position to claim the majority in the Senate, reclaiming Brown’s seat in liberal Massachusetts could be the Democrats’ best chance at holding onto control of the upper chamber. Furthermore, there’s a good chance that the election will turn into a proxy war between pro-business conservatives and progressives looking to scale back Wall Street’s political power. Such a debate could have broad ramifications on other races across the country, including President Obama’s campaign for re-election.

Early polls show Brown narrowly leading Warren, generally by a small number within the margin of error. Whether or not you were offended by Brown’s comments, they served as the first sign that the Massachusetts election will be one to watch in 2012.