Liberal propaganda to attack Bush, basically. He did the exact same thing when the war began, except instead of a stupid message like now, he spammed users with a comic strip portraying Bush in a bad light each time they started up DC++. It's sad that liberals have to go so far as to harrass people just to discredit someone and get the wrong guy in office, but it's his program, and unfortunately, he's going to do what he likes.
As for the "conspiracy" he seems to make it out as, personally, if I were the Bush administration, I'd be doing the same thing. All the voters are in the United States, there's absolutely no reason to have the server's bandwidth wasted allowing people who can't vote to access the site. If Kerry's not smart enough to consider this and do the same thing, it's his problem if suddenly voters can't access the site.
"Good... Bad... I'm the guy with the gun."