Speaking as a Wisconsinite, I'd say that Russ Feingold both proves and disproves your statement. Disproves because he's still pretty poor for a senator, and obeys a higher ethical standard than is necessary(voluntary spending limits, voluntarily telling outside groups to not advertise for him, etc.). He proves it because he originally got elected because the other two candidates didn't take him seriously, and destroyed each other quite successfully through negative advertising. Then, when Feingold took a stand against soft money and his opponent didn't, he won an extremely close election.
He was the only one to vote against the original PATRIOT act, and he voted for John Ashcroft in Bush's cabinet because he figured a president should have the right to choose his advisors.
Sadly, while I could probably name 20+ senators without having to think terribly hard, I am unaware of any other politician who would be anywhere near those standards.
That said, given that Feingold(along with every other senator) dropped the ball on the DMCA, I have no great faith that he'll be all that helpful in at least making a stink about ACTA.