I remember early in the campaign Kerry had huge leads there, even when trailing nationally and sometime in September it flipped and remained a tossup until election day. How come Richardson failed to deliver it when all the pundits said he would?
In addition to what everyone else has told you, one more factor:
Richardson was up against the
other political power in NM, Senator Pete Domenici, who
also campaigned across the state. Domenici narrowly beat Richardson in this knife fight, and won bragging rights until the next election.