It seems like there's some sense of panic in these parts today, which I think is overstated. At some point, negativity can rebound upon the mudslingers. There is a serious chance that this will happen to Bush--in part because observers are starting to see the pattern of how he and the DeLay Mafia did it to McCain, Gore, Cleland, and so many others, and in part because it's just too easy to fire any charge, on almost any issue, back at the accusers. (Indeed, let's talk about military records, national service, and "decades of little accomplishment." By all means.) Maybe I'm naive, but I can't accept that an incumbent who spends three quarters of his time attacking the challenger will ultimately win.
Look at it this way: elections that include an incumbent are generally referenda on the performance of the incumbent. Bush is trying to change this such that, instead, the vote is a referendum on the personality of Kerry! This is, I think, unprecedented.
The plausible deniability of the Swift Boat group and its connection to the campaign is pretty much gone. Bush can't really point to good news from Iraq, on the economy, or anywhere else; Americans really are feeling the "Big Squeeze" David Sirota writes about in the current American Prospect which is why even the intermittent positive data from macroeconomic indicators isn't resonating. People aren't feeling it (unless they're CEOs, in which case their votes, and their checkbooks, are long since spoken for).
Add in better-than-usual money and energy for the Democrats, and the general truth that a majority of undecided voters ultimately will favor the challenger, and it's hard to see how Bush will win. In 2000, he had overwhelming media approval; the press loathed Gore and he charmed them. Not true this time, as even some reliable right-wingers aren't towing the party line on the Swift Boat people and mediots like Matthews are belatedly discovering a sense of professionalism. Also, some in the press must be smarting from four years of mistreatment at the hands of the White House. Aside from Candy "Shelob" Crowley and Judy "Bride of Ashcroftstein" Woodruff, it seems like many of them feel that their pride and credibility are on the line.
In fact, the biggest way I see Bush coming back is if, one, they cheat (which terrifies me), or two, some outside event happens to give him one last short-term bounce, e.g. bin Laden presented on Oct. 31 or Iran attacking the U.S. Even Saudi manipulation of gas prices, or a sudden spike in job creation numbers, probably wouldn't do it alone.
The famous Reagan question, "Are you better off than you were four years ago?" is met with an almost universal "NO!" In the end, that will probably be enough.
Unless they cheat. In which case, we march.