Lots of candidates, lots of reasons:
http://www.slate.com/id/2101383/Excerpt:
John Kerry's Long Shortlist
Who he'll pick as his running mate and why.
By Michael Crowley
Posted Friday, May 28, 2004, at 8:34 AM PT
John Kerry is currently engaged in one of Washington's most elaborate Kabuki rituals: the hunt for a running mate. Every four years, campaigns put vast effort into flattering political allies, pandering to interest groups, generating media buzz, and spreading disinformation. Richard Nixon is said to have advised the elder George Bush in 1988: "Once you get it down to two or three people, see to it that a dozen or so names get out in the press. It'll be a sop to everyone on the list, and it will keep the press off the trail." The press was diverted so well that Bush's eventual choice of Dan Quayle triggered one of the madder feeding frenzies of recent memory.
Also confusing matters is that what used to be the chief rationales for picking a running mate are fading. It's been a while, for instance, since a running mate was chosen to carry a major state. Today's veepstakes involves more sophisticated factors. Here, then, is a taxonomy of some names in heavy circulation and why we're hearing them.