From this article:

Something almost without precedent in America will happen Thursday. That’s the day when McCain-Feingold — aka the Bipartisan Campaign Reform Act of 2002 — will officially silence broadcast advertising that contains criticism of members of Congress seeking re-election in November. Before 2006, American election campaigns traditionally began in earnest after Labor Day. Unless McCain-Feingold is repealed, Labor Day will henceforth mark the point in the campaign when congressional incumbents can sit back and cruise, free of those pesky negative TV and radio spots. It is the most effective incumbent protection act possible, short of abolishing the elections themselves.

Signing this bill was one of those things Bush did that ticks me off. I have no idea what he was thinking here. And then the Supreme Court approved it! Who knew?