Isn’t Media Matters a 503c (not supposed to take part in politics)?
Yes, Media Matters is a 501(c)(3). David Brock also has a “Media Matters Action Network” organized under the 501(c)(4) rules. Both are likely violating their tax-exempt status.
http://www.foxbusiness.com/markets/2011/08/03/media-matters-puts-tax-exempt-status-in-jeopardy/#ixzz1U10kTIEf