That’s more than double his haul of $1.5 million in the third quarter of 2011. Brown also raised his cash on hand from more than $10 million to approximately $12.8 million, according to Cook.

Cook said this was the largest fundraising quarter since the special election in 2010 in which Brown captured the late Sen. Edward Kennedy’s (D) seat.

Cook’s letter to supporters touted Brown’s “independent voting record.”

In recent weeks Brown has bucked his party on a number of issues, supporting President Obama’s recess appointment of Richard Cordray to the Consumer Financial Protection Bureau (CFPB) and blasting House GOP members for botching the politics of the payroll-tax debate.

Brown could be looking to broaden his base of supporters, as his likely opponent will be liberal firebrand (and President Obama’s first choice for the CFPB) Elizabeth WarrenElizabeth Ann WarrenSenate Dems hold floor talk-a-thon against latest ObamaCare repeal bill Trump bets base will stick with him on immigration Dems call for action against Cassidy-Graham ObamaCare repeal MORE (D).

Last quarter Warren trounced Brown in fundraising, more than doubling his numbers, $3 million versus $1.5 million, despite only six weeks of campaigning.

“Despite our success, we also know that our opponent is getting lots of financial support from extreme liberal special interests and she will likely surpass our numbers,” Cook said in his email.

Warren is expected to report her fourth-quarter numbers in the next few days.

The Massachusetts Democratic Party was quick to attack Brown for the haul, saying it’s evidence that he puts the interests of big banks and Wall Street first.

"It's no surprise that Wall Street and the big banks continue to finance Scott Brown’s campaign because he continues to put their interests first, ahead of middle-class Massachusetts families,” said MDP communications director Kevin Franck in a statement. “No amount of Wall Street money can hide his record of voting against job creation, against tax cuts for the middle class and for the radical Tea Party budget plan to destroy Social Security and Medicare."