Actually it could, because there are only a small minority of people that are politically active. What you need to do is start early in the process of candidate selection where fewer people participate. You could effect both major parties and make sure that the candidates that end up on the final ballet from both parties are from your organization. Something like this happened locally here. The police in the area hated the elected sheriff who had been in office for years and years. At the county party convention I'd say about 1/5 of the 400 people there were police officers who all very vocal about their support for the new guy who they picked themselves. The incumbent didn't get enough votes to even make it to the primary election, ensuring that he wasn't an option at the general election save by write-in.
The same also happened to Bob Bennett in Utah too. A small group organized and flooded the local precincts with their members. However, when Orrien Hatch came up for re-election he was wary and careful to flood the precincts with hundreds of people. Usually a precinct elections will only have 20-30 people show up, but that time there were over 150.
The lesson is that it can have an effect, but not only as a surprise tactic.