This is a common euphoric moment between the challenger's convention and the incumbent's. It's the bounce, stupid. Remember how Gore was way up in the polls at this point four years ago?
I still think the fundamentals are there for Kerry to pull it out, maybe by a lot, but this euphoria is way premature. First, it's highly likely that the Republican convention will produce a Bush bounce (do I hear anyone predicting the 15% the Bushies predicted for Kerry?). Republicans are good at TV events, and they are working hard to put their more sensible, moderate wing front and center while keeping the frightening types in the closet.
If the post-convention bounce is likely, the next thing is a dead cert: there is one absolute constant in the Bush family M.O. when threatened electorally—go deeply negative, ideally via surrogates. I first saw this in action in the Republican Presidential primary in Connecticut in 1980, when for a time it looked as John Anderson might carry one of GHW Bush's several home states. All of a sudden anonymous fliers, mass telephone calls, and ads on small radio stations blanketed the state making false allegations against Anderson such as that he wanted to eliminate social security. And all of a sudden GHWB's poll number bottomed out.
Indeed, it looks to me as if the smear campaign is already well under way. If the Kerry people know how to respond to this beyond posing with generals and other veterans (which is good, but not enough), they've yet to demonstrate it. It's always possible the voters will rise above this sort of smear, or that the press will treat it sufficiently critically to defang it, but 'hope is not a strategy'.