The FEC can do whatever the Hell they like, but they will find that unless they intend to restrict the Internet as does Communist China (hand in hand with Google, Yahoo, MSN, etc.), political speech and blogs online cannot be regulated. As some posters have suggested, there will simply be a mass migration of bloggers to foreign servers where McPain-Foolsgold and the FEC cannot touch them.
As for the legal battle within the U.S.? Who do you think will be the most powerful ally for bloggers in putting the kabosh on the FEC and other government agencies?
Ironically, it will be the dying MSM, because as they seek to recover lost subscribers by increasing their online web presence, any restrictions on Internet-originated political speech will be tightening the noose even further around THEIR necks. For that reason alone, they will pour their not-inconsequential legal resources into this fight.
And if they do manage to somehow shut down or restrict the access of American citizens to Constitutionally protected free speech online?
We should remember the patriotic example set by a pre-Internet patriot, the late Reverend Dr. Carl McIntire, and his offshore broadcast operation, "Radio Free America":
http://www.carlmcintire.org/columbus.php
And McPain?
We'll shove the broadcast mast all the way up your traitorous ass until it tickles your tonsils.
The 'net via bloggers and forums is the main reason the asinine media is dying.