We're just over four weeks from a midterm election that could result in a major power shift in Congress. What is new this year is the way the campaigns are being conducted, and how much is being spent - not by the campaigns themselves, but by others: corporations, advocacy groups and individuals with deep pockets. Media analysts estimate a record-breaking - and jaw dropping - $3.7 billion will be spent on advertising alone. But by whom exactly? The 2010 "shadow campaign," as some are calling it, is on Need to Know's "Watch List" this week. Need to Know airs Fridays on PBS.