Scott Brown's 2010 victory was seen as a coup for the Tea Party — and he encouraged that interpretation. After winning the election, he would sign autographs by scrawling the number "41"; a reference to the fact that he could provide the crucial 41st vote needed to filibuster Democratic initiatives.

Fast forward two years, and Brown is basing his campaign for reelection in part on the times he's been the crucial vote for the Democrats. His main example is the Dodd-Frank financial regulation bill, where he was only one of three GOP senators to vote with the Democrats. "It never would have passed if it wasn’t for me," he told MSNBC this year. "I was tired of having banks and Wall Street act like casinos with our money."

(Associated Press)

Meanwhile, Elizabeth Warren is basing her campaign on the idea that Brown and the Democrats didn't go far enough, and that she would go significantly further. She boasts of her role in creating the law's new Consumer Financial Protection Bureau, which has been one of the most visible (and politically controversial) changes so far. And, in the wake of JPMorgan's $2+ billion trading loss, she has called for the reinstatement of Glass-Steagall, arguing that "banking should be boring" and should keep risk-taking trades separate from ordinary consumer banking.

She's also calling for federal enforcement officials and state attorneys general to investigate and prosecute banks "whose illegal actions have broken the economy." If elected, she would become one of the most visible voices on Capitol Hill for progressive action on financial reform, at a time when many on the left have been disappointed with the limited reach of Dodd-Frank.

Warren accuses Brown of doing Wall Street's bidding both before and after his vote for the bill. Brown used his political leverage during the Dodd-Frank debate to secure the removal of a $19 billion tax on banks to help pay for the bill. He also helped carve out changes in the Volcker Rule to secure an exemption for mutual funds — which have a strong presence in Washington — in Massachusetts, and successfully lobbied to allow banks to continue investing a small portion of their capital in hedge funds and private equity, despite the increased risk associated with those assets.

Brown has also lobbied regulators after Dodd-Frank was passed. In March 2011, Brown's legislative director asked a Treasury official to interpret the rule on hedge-fund and private equity investments more broadly, and Brown himself made a later appeal, as the Boston Globe first reported. But Brown denies that he was trying to roll back the provision. "Senator Brown's staff was offering thoughts on Senator Brown's interpretation of the actual legislative intent," Reed said. And his campaign defends his role during the Dodd-Frank negotiations, stressing that Brown "broke with his party to cast the deciding vote."

Brown and Warren are tied at 46 percent, with 49 percent of voters calling Brown "an independent voice for Massachusetts," according to the latest Pubic Policy Polling survey. "He's piecing together the [bipartisan] votes he has taken to cross over" to independent voters," says David Paleologos, director of the Suffolk University Political Research Center in Boston.  And Dodd-Frank is "one of the links" that Brown has to Democrats in a state where 27 percent of Obama voters already support him, Paleologos adds.

In what Paleologos describes as a "1 percent race," Brown is trying to keep the national GOP at arm's length, and his campaign for Dodd-Frank is a prime example of his independence. "Senator Brown believes it should be implemented as its authors in Congress intended, and that's exactly what Senator Brown and his staff have consistently advocated," his campaign spokesman Colin Reed tells me. "For instance, Brown did not join the Republican filibuster of Richard Cordray and supported the President's recess appointment, which was forced by unprecedented obstructionism.  Senator Brown worked across the aisle with Rep. Frank and others to save Massachusetts jobs — workers that had nothing to do with causing the financial crisis."

The campaign adds that Brown "opposes efforts to reduce funding" to the SEC and the CFTC, noting that both have taken on more responsibilities under Wall Street reform. And if he's reelected, he will be one of the lone GOP voices left in Congress to defend Dodd-Frank, particularly with the departure of Olympia Snowe, one of the two other GOP senators to vote for the bill.

Incidentally, he no longer signs autographs with the number "41."