He won one term because he did not show much interest in campaigning against Clinton until about 2 weeks before the election.
A couple of weeks after his loss, a reporter asked him why he didn’t campaign much. His response was that, as the incumbent, he thought he would win against the governor of Arkansas, so he didn’t see the need to campaign.
As the polls narrowed, he finally started, but it was too little, too late. And the ‘read my lips’ broken promise didn’t help him much either.
Bush was the pro at clutching defeat from the jaws of victory. The GOP followed suit ever since.