Hyannis, Massachusetts (CNN) -- Massachusetts Sen. Scott Brown rode into office two years ago as an everyman with a pickup truck, vowing to "take back the peoples' seat" held by Democrat Ted Kennedy for nearly half a century.
Here on Cape Cod, Brown's breezy persona persists as he strolls down Main Street, shaking hands, posing for pictures and playfully shouting to a passerby to keep her eyes on the road.
But the junior senator's attitude belies a stark reality: He is in the midst of a contentious race with a liberal icon who recently won the state Democratic convention with a record 95.7% of the delegate vote.
Elizabeth Warren, President Barack Obama's high-profile consumer advocate and a Harvard Law School professor, is seeking to take back the seat Brown snatched from the Democrats in a special election in 2010 after Kennedy's death.
In an era in which bipartisanship is a dirty word in politics these days, it's never far from Brown's lips, recurrent in his ads, and most importantly, evident in his votes.
No matter the question to Brown, he tries to weave in that he is the "second most bipartisan senator" into his answer. (That comes from a ranking in a congressional publication).
While most of his Republican colleagues boast about blocking the president's agenda, Brown brags about helping.
"I can name a litany of Democratic-sponsored bills that never would have passed had it not been for me," Brown told CNN. "The president had called me. The vice president calls me. Secretary [of State Hillary] Clinton calls me for my vote all the time."
Departure from GOP on health care ruling
In the wake of the Supreme Court decision upholding the president's health care law, Republicans jumped on Chief Justice John Roberts' conclusion that the health insurance mandate is a tax.
Brown, once again departing from his party's central message, said he disagrees with the Supreme Court's decision calling the individual mandate a tax.
"I voted for the bill here in Massachusetts and never thought of it as a tax and to all of a sudden think that the federal one is a tax is just not appropriate," Brown said. "I disagree with the Supreme Court and what the party leaders in Washington and others are saying really has no bearing on what I'm doing."
Still, Brown and the president hardly agree on the Affordable Care Act.
Brown was elected on his promise to work to repeal the massive health care reform law, making it his main battle cry in the special election.
Though he voted for Massachusetts's health care mandate, which was made law in 2006, Brown said he disagrees with the national law, arguing that health care should be a state issue.
Warren a Democratic heroine
Brown's challenger does not want to repeal the health care law, saying it has been passed by Congress, signed by the president and now deemed constitutional by the Supreme Court. Like Democrats across the country, she says fighting yesterday's battles is a waste of time and energy.
Warren is a Democratic heroine who gained national notoriety as architect of Obama's Bureau of Consumer Protection this year. Despite many years of experience in Washington, this is her first campaign. But she's a quick study in pressing the flesh on the campaign trail.
"I never thought I'd run for public office, but I got pulled into this because of the urgency of this moment. Families are getting hammered, and they can't take it much longer," Warren told CNN inside her Brookline campaign headquarters.
She's got her message against Brown down pat.
"Scott Brown stands with the billionaires and says they shouldn't have to pay more in taxes. Scott Brown has been standing against working families," said Warren.
Question over Native American heritage
But Warren has stumbled over an issue that she admits tripped her up.
When the Boston Herald reported that Harvard University had touted Warren as a minority faculty member, she said she knew nothing about it.
But after weeks of questions from the media and accusations by her opponents that she claimed minority status to advance her career, Warren admitted that she had told Harvard and the University of Pennsylvania about her heritage after she had been hired, insisting it was not a factor in her hiring. Warren's campaign could not tell us how Warren made her employer aware of her Native American background.
Warren also said that she had listed herself as part Cherokee in professional directories in order to meet people with similar backgrounds.
"I listed myself in the directory in the hopes that it might mean that I would be invited to a luncheon, a group, something that might happen with people who are like I am. Nothing like that ever happened, that was clearly not the use for it, and so I stopped checking it off," Warren told reporters in May.
As a first-time politician, Warren admits she could have responded faster.
"I was really surprised that anyone wanted to make this a political issue. I was really surprised by that and very slow to respond to it," Warren said. "I'm like every other kid. I learned about my family from my parents."
Warren explained she heard stories from her parents about having to elope because her father's family did not accept her mother's because of her Native American roots.
"My mom and dad were very much in love. They grew up in a little town that had been Indian Territory just a few years earlier. When they wanted to get married, my father's parents said no because my mother was part Cherokee and part Delaware. And my parents fought it as long as they could and finally they eloped," Warren said.
"I lived with that, between two families," she said.
But Brown has not backed down, insisting that Warren's failure to explain herself from the beginning calls her integrity into question.
"When you run for high elected office you have to pass a test, and that test is one of honesty, trustworthiness and truthfulness, and she's failed that test," Brown said.
He continues to call on his opponent to release confidential documents to show whether or not she claimed her Native American roots on job applications.
A Republican source even gave CNN a copy of Warren's mother's death certificate, which listed her as white, not Native American.
Asked about that, Warren simply repeated that her parents "grew up in a very different time."
"They grew up in a little town that had been Indian Territory. My mother's family was part Cherokee and part Delaware. That's who they were," she said.
Harvard administrators said they did not know about Warren's ancestral claims when they hired her. And Warren bristled when asked if she considers herself a minority, saying simply that she is proud of her heritage.
"This is part of who I am. This is who I am," she said.
Warren said Brown is distracting from issues that really matter to people.
Asked whether he and other Republicans are engaging in divide and conquer politics, Brown responded that he is engaged in issues that touch people's lives "every day."
"With all due respect, I'm getting things done," said Brown.
Justifying money from Wall Street
To be sure, Democrats have their own arsenal of opposition research against Brown that they're beginning to dip into.
In one of Brown's television ads, he touts being the deciding vote that allowed Wall Street reform to pass the Senate.
But the Boston Globe reported an aide e-mailed the Treasury Department after that bill became law to try to make sure restrictions on big banks ended up as loose as possible.
Brown told CNN he "respectfully disagrees" with that report.
"The e-mail was simply trying to make sure the Treasury did what Congress wanted it to and not have unelected, unaccountable bureaucrats circumvent Congress and have new rules and regulations. I'm very comfortable with where I am on that," said Brown.
Warren's campaign also regularly notes that Brown is flooded with campaign donations from Wall Street.
According to the nonpartisan Campaign for Public Integrity, Brown has received nearly $2.5 million from the financial and real estate sectors, more than any other senator in either party.
Brown has no apologies.
"I'm raising money like every other member of Congress, like every other member of the delegation, and like Professor Warren, and for her to say that taking Wall Street money is a bad thing -- we have the No. 2 financial services market in the entire country. I'm going to advocate as I've done from day one that they're not caught up in that mess that they had nothing to do with," Brown said.
Warren, who made her name blasting big banks run amok, may not be raking in cash from Wall Street, but her fundraising figures are something to behold.
Her campaign announced this week she raised $8.6 million in the second quarter of this year alone, dwarfing the $1.7 million she raised in the first quarter.
Though Brown outraised Warren in the last quarter, he fell far short of her total this time. His campaign announced Wednesday that the senator raised $5 million in second quarter of the year, up from the $3.5 million he raised in the first quarter.
Deal: No money from outside groups
The two will have to keep raising big dollars in order to abide by a unique agreement the candidates made to discourage outside groups like super PACS from advertising in Massachusetts. Under the deal, if an outside group runs an ad on a candidate's behalf, he or she must give 50% of the cost of the advertising buy to the charity of the other's choosing.
It's unclear how long that deal will hold, given the fact that this is the most closely watched Senate race in the country, and the latest polls show the two candidates are neck and neck.