Why did Gore do it? One angle unexamined so far is the psychology of polbots–men who have been trained from youth for political careers. Politics is a harsh mistress; following her in youth makes her even harsher. After decades of self-discipline and deprivations, the experience of being repudiated by the voters, especially in a presidential run, has powerful and disturbing effects.
John Quincy Adams, the original polbot, managed to succeed John Adams, his father, in the White House in 1824. But he was crushed in his re-election bid. The remainder of his life formed a strange coda. JQA got to the White House by embracing national expansion, tying himself to southerners (Madison, Monroe, even for a time Andrew Jackson), and zipping his lip on all questions related to slavery. After some brief post-defeat floundering, he became a congressman, in which role he fought expansion, flayed the south, and spoke endlessly against slavery. JQA II was arguably better than JQA I–but he was certainly different.
Al Gore seems to have done a similar thing, revealing an id repressed during years of political office-seeking. Now that his ambition has been swatted down, out it all hangs.
Would GWB have some similar crisis if he lost in 2004? Perhaps not: he spent less of his early life pursuing the job (Jeb was the ordained successor). He has also already had his life changed, on 9/11.