NH Rep. Carol Shea-Porter (D) has been underestimated before, much to the chagrin of former GOP incumbent Rep. Jeb Bradley, whom she upset in 2006 and edged out again last year. But Republicans say her last two general election wins were helped by strong Democratic waves nationally, a factor that may not be in play next year.

If so, the GOP's hopes for a Northeast comeback may end up riding on Manchester Mayor Frank Guinta, who filed paperwork last week to form an exploratory committee for a Congressional run. One of the state's few prominent Republican officeholders after the retiring Sen. Judd Gregg, Guinta has been mentioned frequently as a potential gubernatorial candidate. But with popular Democratic Gov. John Lynch likely to run again, the National Republican Congressional Committee also identified him as a top recruit for a House race.

What makes Guinta's candidacy so enticing is his home field advantage in the Queen City. Though Manchester is a majority Democratic city, he won a second term in 2007 by nearly eight points, and raised record funds in the process. Manchester also played a key role in Shea-Porter's last win. She carried every ward last year and took the city by 5,000 votes -- accounting for 40% of her reelection margin in the 1st Congressional district. No wonder Republicans hope Guinta's special appeal for the city's voters could be the X-factor in next year's House race.

A Guinta campaign adviser said that the greater Manchester area accounts for 37% of the vote in the House district and Guinta's popularity and standing in the city will "be a huge advantage." A new University of New Hampshire survey released this week presented some additional warning signs for the incumbent. Shea-Porter's approval rating remains under 40% in the district, while her disapproval climbed to 35% -- her worst since taking office. Her favorability rating in the Manchester area is actually the lowest of any of the regions surveyed -- just 29%. Compare that to Guinta, who has a 52% favorable rating there.

Shea-Porter's problem, Republicans say, is a voting record more liberal than her constituency. And even Democrats gripe about her lackluster fundraising. Unlike last year, Shea-Porter is "actually going to have to run on her own," the Guinta adviser said, noting the boost provided by Barack Obama's strong performance in New Hampshire in 2008.

Guinta plans officially to announce his candidacy next week.