Voter fatigue. I ran into many of such people. Just tired of politics, all the ads on TV. When that happens, the race will go to the superior GOTV efforts. The Democrats are MUCH better at that then the GOP. That is probably the bottom line. You can talk principles and ideals all you want, but it all depends on who actually gets their people to vote, and they do it much better than we do.
There is a rule of politics that massive negative ads by both sides are neutral but have the effect of lowering turnout.
That may be a part of the hidden story of 2012.