The sum is made up largely of donations of less than $250, and Shaheen received contributions from nearly 8,500 donors, her campaign said.

“Senator Shaheen is both proud and humbled to have so much grassroots enthusiasm behind her and her efforts to strengthen New Hampshire’s small businesses and middle-class families,” said Shaheen's campaign finance director, Andy Darkins.

Though she's running in a swing state where Republicans believe they could have a shot at her seat without President Obama at the top of the ticket, Shaheen has shown resilience, with a February poll revealing 59 percent of New Hampshirites viewing her favorably.

And no Republicans have yet emerged to challenge her. Former Reps. Frank Guinta and Jeb Bradley are both said to be looking at a run, but either could choose instead to challenge Rep. Carol Shea-Porter (D), who is considered the most vulnerable of the state's Democratic officeholders. Former Sen. John Sununu could also run, but he hasn't yet made a bid official.

Shaheen could have a bit of a headache, however, if former Massachusetts Sen. Scott Brown (R ) chooses to run. He left the door open to the possibility recently, and his strong fundraising ability could match, if not exceed, Shaheen's war chest. But he'd face an uphill battle convincing New Hampshire voters he isn't just carpet-bagging into a seat, and he could be more inclined to spend some time in the private sector before running again, or looking at the Massachusetts gubernatorial race in 2014.