Independent political organizations known as "super PACs" are the wild cards in this year's election, the product of a series of court rulings, including the Supreme Court's Citizens United decision in January 2010. A total of 38 super PACs have spent $58.7 million -- 56% of which has been spent opposing candidates.
Here's a look at the spending to date, in support and in opposition, according to reports filed with the Federal Elections Commission.