A small but dedicated regional or national group of people can have a
devestating impact on a congressional race. I've been a part of this kind of thing before, and it is a beautiful thing to behold.
Basically, we pick a few vulnerable congressmen on the opposite side of an important issue -- say HR 1955

-- and basically end their political careers for them, light a bolt from the blue.
A sudden, massive grassroots effort originating from outside any campaign, and concentrated on one little district can be the political equivalent of "shock and awe". As a bonus, we automatically elect someone who knows who got them into office -- us!
After that, if our movement gives a friendly call to any congressman over some issue important to us, you can bet they'll take our call (after they change their Depends.)