The 2004 election was the first to be affected by the campaign finance reforms mandated by the Bipartisan Campaign Reform Act of 2002 (also known as the McCain–Feingold Bill for its sponsors in the United States Senate). Because of the Act's restrictions on candidates' and parties' fundraising, a large number of so-called 527 groups emerged. Named for a section of the Internal Revenue Code, these groups were able to raise large amounts of money for various political causes as long as they do not coordinate their activities with political campaigns. Examples of 527s include Swift Boat Veterans for Truth, MoveOn.org, the Media Fund, and America Coming Together. Many such groups were active throughout the campaign season. (There was some similar activity, although on a much lesser scale, during the 2000 campaign.)

What finance act affected the 2004 election?