"Swift Boating" seems to be in the news this week, so here's my quick contribution:
Swift Boating -- and the George W. Bush campaign in 2004 in general -- was probably a dud. The most important thing to know about the 2004 election, when it comes to electioneering effects, is that Bush underperformed the "fundamentals" models.
Nate Silver has conveniently gathered some of the numbers on this. Of the 15 prediction models he collected, 14 picked Bush as the winner, and of those 13 predicted a larger margin of victory than the 2.4% that Bush won by. The three predictor systems (Hibbs, Abramowitz, Wlekien and Erikson) that have performed best over the years all picked Bush, and by anywhere from 3.4% to 7.5%. I don't really put a whole lot of weight on the other systems, but for whatever it's worth they generally erred even more on the side of a big Bush win.
It's far short of proof, and of course it's certainly possible that one part of the campaign was a success but that another part was an even larger failure. But overall it suggests to me that anyone who believes that the Bush campaign did a better job than the Kerry campaign in general, or that the Swift Boat smear in particular helped Bush in any significant way, must meet an even higher burden of proof than if we didn't have this additional evidence. In particular, it just won't it to say "Bush won" as if it's an argument clincher. What really appears to need explanation is why Bush did worse than he should have, not why he won.
I'm going to get into this in more detail later, but that's the bottom line: there's no good reason to believe that the George W. Bush campaign in 2004 was responsible for his victory.