He isn't the "big reason" President Bush won.
President Bush did that on his own. Blackwell just made sure that the rules in place were enforced.
Mike, the original poster said "a big reason" and not "the big reason". And I agree - Blackwell knew Ohio was being targetted by the DNC theft machine, and he made sure that the state ran a clean, uncontestable election and stood up to any 'rats (or their surrogates) who tried to create phoney controversy.
Bush won on his own (with help from the RNC and state organizations, of course), but Blackwell was a key guy in making sure the win actually counted.