Sean Bielat isn't the type of candidate who could win a congressional race here, even if he wasn't facing a Kennedy.
I don't really see how he's particularly unelectable by the standards of MA Republicans. Of course, it'd be a stretch for anyone with an (R) after their name to get elected anywhere in MA.
(Though the MAGOP is so fail, topping off not even running candidates in over half the state house races with nominating a child molester and a birther in their two top congressional pick-up opportunities).