On Sunday, Madison's Monona Terrace hosted a rally for the Americans for Prosperity (AFP), a "grassroots" nonprofit founded and funded by billionaire industrialist David Koch.

MADISON -- With polls showing Wisconsin Senate candidates Tammy Baldwin and Tommy Thompson in a statistical dead heat, Obama swept into Madison, Wisconsin for an early morning rally on his final day of campaigning. The Obama campaign hopes to lock up the state and give a boost to Baldwin, as the candidates addressed a wildly enthusiastic crowd against a backdrop of blue skies and a white State Capitol building, that looks a heck of a lot like the U.S. Capitol. On the plane with Obama, one of his most effective bridges to those few remaining undecided voters, Bruce Springsteen.

"Dark money groups" that do not disclose their donors not only refuse to be transparent about where they get their money, in many cases they are not transparent about how they spend it. Dark money only accounts for about one-quarter of the over $1 billion in outside election spending reported to the Federal Election Commission, but because of gaps in reporting requirements, the actual percentages -- and the actual totals for outside spending -- are certainly much higher.