Bernstein revisits the 2000 election. He thinks that the state of the economy played a large role:

For better or worse, what political scientists have found is that voters have very, very short memories; the models that work best only look at election-year economic factors.  So Gore apparently got little credit for the boom years.  Moreover, what seems to matter isn't unemployment, or general economic growth, but changes in real disposable income.  And as it happened, GDP growth continued through 2000, but growth in real disposable income stalled that year, heading into the 2001 recession.