A ProPublica investigation shows that many 501(c)(4) nonprofits active in the 2010 election spent millions of dollars on campaigns, sometimes reporting less political spending to the Internal Revenue Service than they did to election officials. Some groups listed here – including several with long histories and well-established social welfare missions – put only a small portion of their resources into politics and reported accurately. How we calculated these numbers | Related story »

Suevon Lee and Jonathan Stock contributed research for this project.See all organizations »