Aborted Political Trends in the United States?

Exactly what it says in the title. Are there any good examples of what seemed to be emerging trends in United States politics that were quickly reversed, or otherwise never quite came to fruition? Say, a demographic group that was slowly trending away from one party over a period of time before largely going back? Or a time when one of the major parties seemed to become more receptive to a new ideology before backtracking?
 
Top