I find him to be a highly intelligent and intuitive person and a politician with the quickest learning curve we've seen in this generation.  I don't think he would have run this go around if he had not felt he could win this go around.  He may even have surmised that this truly is his best and only shot.  I take him at his word that he will not run again for President (unless it is as the incumbent President).  In fact, if he loses, I'd expect he'll run for Governor of Illinois and be quite happy in that position.

And I think he also rightly deduced that there is, indeed, "a fierce urgency of now."

He will stick with being an elder statesman and global warming evangalist, which is what he does best.  Frankly his credibility as a candidate in 2000 came from his service as VP, i.e. he was trading on his connection with Bill Clinton, putting him in the same boat with Hillary Clinton's 2008 run.