The problem is how deeply gerrymandered his district is... I live here, so I know.
The northern part is Newton, Wellesly & Brookline - which is nothing but wealthy liberals. It travels south, taking the narrowest path possible through the I-495 corridor, which tends to be conservative - to end in New Bedford, Fall River and surrounding communities which is all fishing, factory workers, with heavy immigrant populations, who vote Dem because the area newspapers tell them to. Frank also represents Dartmouth, which is home to UMass Darthmouth - a major college. Frank also covers a few small towns in this area which trend conservative, such as Fairhaven and Westport, as well as a few sleepy townships, but the population count is meaningless compared to Fall River and New Bedford, and the imported college kids.
In short, beating Frank is a daunting task, and was intentionally designed to be so. The best we can hope for is depressed turnout, maybe assisted by a nice bigass Noreaster. I'm hoping the VWRC considers unleashing the weather machine to nuke Frank's campaign - I filled out the appropriate forms, but you know how it is, especially around electioneering season...