Perhaps a ford presidency lasting to 1981, with Rockefeller retained as VP? This would give Reagan the nomination in 1980, but party fatigue would have been kicked into overdrive. This could be enough to have a democrat win in 1980. We will just say Ted Kennedy, since he nearly won the nomination anyway. Then somehow, have a more moderate George HW Bush win in 1984, and hold the presidency until 1993. This would, in essence, create an at least more socially moderate GOP, perhaps socially liberal, but probably not progressive.