I agree with earlier posters about the act of political sabotage that Hitchens is trying to instigate. I have to wonder what level of reverse psychology is operating here. A fake distraction from Hillary, the neocons' preferred target? Breaking Gore against her campaign machine now that she seems a shoo-in to take him out for later? Or just sullying his position of credibility on the issue he cares so much about?
I think that Gore stands to lose that, if anything, by making a run for President. He would lose his focus on the environment; it'd undoubtedly take a back seat to foreign policy, how could it not? And if it does, policy change on the environment is likely delayed for who knows how many more years. And we know who benefits from that kind of stalling.
Gore is in a position of not having to compromise, by virtue of not having a personal stake in the election. So far he can tell us his opinion, polls be damned, and that could change were he to run for President. His opinions might not change, but I'd expect to see their expression get toned down.
So to reiterate what the others have said, he has more power to make change in environmental policy where he stands now. Hitchens' claim that Gore 'never had the stuff to do the job' if he doesn't run is simply a dare. I dare you to run. You're a wimp if you don't run. Feh.
I'd support Gore in '08 (I'd support a warm corpse or a friendly border collie marked "D" over any Republican), but I hope he doesn't bother. I think he can do more from outside DC, and I think he knows this.