The 1988 Presidential landslide upset:
https://www.theatlantic.com/past/docs/politics/policamp/insider.htm
"It's fairly easy to find evidence for the theory that the Democrats are headed for a victory. Just look at the polls--and not only the "horserace" polls, showing Dukakis with a healthy lead over Bush. Gallup polls taken earlier this year showed the Democrats regaining a lead, of 42 to 29 percent, over the Republicans in party affiliation."
What killed it for the Democrats? Crime... Willie Horton, debate rape question and the embarrassing photograph of him in a tank taken on September 13, 1988, which subsequently formed the basis of a successful Republican attack ad