Following immediately on the heels of Bush's acceptance speech, Kerry's speech (which was probably more or less intended as a rebuttal, which is more or less unprecedented — candidates generally don't respond to what goes on at their opponants' conventions) seems amazingly petty and backward-looking. Going straight from Bush's broad plans for the future (tax reform, private health-care and retirement accounts, the spread of freedom throughout the globe through the coming century) to Kerry whining essentially that “I should be president because IIIII was in Viiieeeetnaaaaam, and Cheney wasn't!” hits like a sledgehammer. No guarantee that the media will play the good parts of Bush's speech, so this contrast may not show up to the broader public, but for those who are paying attention, this basically says to the world that Kerry is not interested in engaging his opponants on the issues; he'd rather stick to Vietnam.
The President's speech was a brilliant speech, and excellent strategically as well. He never mentioned Vietnam, he stuck to issues, and gave exciting new ideas. Kerry missed the opportunity to praise Bush for sticking to the issues, and responding with his own views to shift the dynamic of the race so that issues were what it was about. With the laws saying that 527 groups like Swift Boat Veterans for Truth cannot run ads within two months of the election, Kerry could easily have shifted focus from damage control on something that happened 30 years ago to why people should vote for him. Staying with Vietnam instead is foolhardy at best, and may well cost Kerry the election.
Historically, incumbent Presidents get reelected. If they don't, it's because they did an awful job at something (Carter's bungling of the Iran hostage situation and foreign policy in general, Bush 41's failure to see that it was the economy, stupid) and their opponant has run a campaign that focuses solidly on policy — presenting a definite plan and exciting ideas that make people willing to sacrifice the sense of stability that they would gain from keeping an already known President for another term. Kerry has consistantly failed to do this. He can get a good deal of mileage from the simple fact that he is not George W. Bush, but when it appears that he has no real plan for important issues other than to sit in the Oval Office not-being-Bush, he's going to lose support from people who may not like Bush, exactly, but don't really see any reason to swap horses in the middle of the stream.
Overall, if tonight is an indication of how the next two months are going to go, Kerry will lose –quite possibly spectacularly.