The right wing of the DNC (i.e., the Clintonian Democrats, New Democrats, whatever they're calling themselves now) conspired to offer up someone who is a fine legislator, but who didn't have a snowball's chance in hell to defeat a popular wartime incumbent.
He had better than a snowball's in hell chance. His defeat was extremly narrow in the anals of history, and if someone had a time machine, there wouldn't be that much tweaking neccessary to make him win, unlike some other losing candidates. In the last 100 years, few losing candidates did better than he.