The results from the Show Me State are finally in, and it turns out that McCain beat Obama in Missouri by a paltry 3,632 votes. It may be a minor detail, true enough, but it's worth noting that Ralph Nader and Matt Gonzalez pretty much handed John McCain this victory. Take a look at the certified results. Nader nabbed 17,813 votes – and it's hard to believe that many of these voters were chosing between Nader and McCain. On the other hand, Bob Barr and Wayne Root scored 11,386 votes – votes that might well have gone to the GOP. Subtract the Barr vote from the Nader vote, and you find over 6400 likely Democratic votes – enough to tilt the state to Obama.
I haven't checked other close states to see if third parties would have made a difference. But both Nader and Barr can now claim their candidices made a difference…though hardly a significant one. It's worth noting that while third party candidates are still unlikely to win a race, their presence always holds the potential to be consequential.