Spending money on political campaigns

Which groups spent the most money in the 2010 mid-term elections? Even though the elections were won overwhelmingly by Republicans, three of the top five money spenders were union groups raising money for Democrats. By far the biggest spender was the American Federation of state, county, and municipal employees. Here is a chart from the Wall Street Journal.
via http://mikesamerica.blogspot.com/2012/06/debunking-dems-excuse-for-losing-in.html