Negative ads with a Halloween twist hit the airwaves

Corporate contributions to groups rare

Contest is No. 1 among outside spending groups

Normally negative GOP spending groups show softer side of Mitt

Bauer-backed super PAC assails president

Super PAC donations flow, Ameritrade founder give big.

A primer on the Supreme Court case that changed the way money could be spent in elections.

Nonprofit social welfare organizations may become more potent political donors than super PACs. And they don't have to disclose who gave money.

Why it's so tough to expose super PAC mystery donors.

The New York mayor's new super PAC isn't the first time he's tried to change things nationally and around the world.