Never underestimate the power of incumbency. In our entire history, only nine Presidents did not win re-election,
three of them in my lifetime and only five in the last century. Of those, Taft likely lost because TR split the Republican vote
when he ran against Taft in the Progressive Party.
All four of the others - Hoover, Ford, Carter and Bush - almost certainly lost because of a bad economy.
And despite what pundits will tell you, I think Clinton beat Bush because of Perot - because he won with only 43% of the vote.
And I even voted for Perot.
But even against a still popular Perot, a lost House of Representatives and the failure of Hillarycare - he STILL won re-election.
(BTW - the House re-election rate is phenomenal - despite large 40 seat swings in these big shifts on power - it hasn't dropped
below 80% in my lifetime, and typically is above 90).