"Electability" is a crock. John Kerry was supposedly the most electable Democrat, but what liberal today doesn't wish *someone else* had been nominated in 2004?
Many, I'm sure, but someone like Howard Dean would have lost by a significantly larger margin than Kerry did. Further, considering how little Edwards added to the ticket, I doubt he would have done much better than Kerry, either. Wes Clark was not ready for prime time, and it's not even worth mentioning Kucinich, Sharpton, or Moseley Braun, all of whom would have given Bush a minimum of 45 states.
Of the field, only Gephardt could have—and likely would have—beaten Bush.