Details here; an excerpt:

[T]estimony has revealed a widespread and concerted effort on the part of Republican Secretary of State Kenneth Blackwell to deny primarily African-American and young voters the right to cast their ballots within a reasonable time. By depriving precincts of adequate numbers of functioning voting machines, Blackwell created waits of three to eleven hours, driving tens of thousands of likely Democratic voters away from the polls and very likely affecting the outcome of the Ohio vote count, which in turn decided the national election.

Let us suppose this all turns out to be true; it would still be the case that Bush won the popular vote nationally, and that fact stands as an eternal indictment of the moral sanity of the United States.