Sort of echoing and answering Josh, I do think the corruption stuff has helped make people think, in an abstract sense, "Republicans bad, Democrats not as bad," and has helped give Democrats their massive lead in generic congressional ballots.
However, the more the corruption issue is what's driving the generic ballot lead the worse it actually is for Democrats. Those Democrats who can hang corruption around a Republican incumbent in a tangible concrete way will be able to run with it successfully, but for everyone else it'll be a wash. So, yes, corruption has mattered for the national picture but it won't be enough for the local picture except where people believe that their own member is corrupt.
