Apparently, the working theory is that they wanted to vote in Congressional and local office elections, but hated the Presidential candidates so much that they just declined to vote. Mostly in Detroit.
Does that sound realistic or reasonable to you?
Anyway, our main man on electoral issues, Brad Friedman, lays it all out for you on his indispensable and incredibly important website. You should sign up for his daily emails, listen to his daily audio show, and contribute to his work. This guy is the real deal.