Bitcoins have gone from an Internet oddity to much more. The FEC is now considering allowing the virtual currency to fund some political campaigns. Rick Bowmer/AP hide caption

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A composite image shows part of the NPR/Center for Responsive Politics reporting team's whiteboard at NPR headquarters that was used to map out how Wellspring connects to other social welfare groups. (Click the enlarge button to see a full-size image.) John W. Poole/NPR hide caption

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NPR News Investigations

Secret Persuasion: How Big Campaign Donors Stay Anonymous

Tax-exempt social welfare groups have become the vehicle of choice for big political contributions.

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The Au Sable River in Michigan is a popular place for fly fishermen and the heart of a debate unexpectedly influenced by largely invisible social welfare organizations. Christine Arrasmith/NPR hide caption

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The Olmsted Locks and Dam project is under construction on the Ohio River between Illinois and Kentucky. U.S. Army Corps of Engineers hide caption

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