Interest groups are spending five times as much on the 2010 congressional elections as they did on the last midterms, and they are more secretive than ever about where that money is coming from

The $80 million spent so far by groups outside the Democratic and Republican parties dwarfs the $16 million spent at this point for the 2006 midterms. In that election, the vast majority of money - more than 90 percent - was disclosed along with donors' identities. This year, that figure has fallen to less than half of the total, according to data analyzed by The Washington Post.

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