I have two especially unhappy memories of Republicans achieving serious power -- Gingrich in the mid-1990s, Bush after 2004. They're followed by two happy memories of Republicans getting in serious trouble after attacking popular Democratic social programs -- Medicare and Social Security. In both cases, politically savvy Democrats (Bill Clinton and Nancy Pelosi) firmly defended the programs and won.
I wonder if this is a structural phenomenon. Democrats pass a well-designed program. It becomes popular with swing voters. But there's enough influence in the Republican Party against it that when Republicans come to power, they have to attack it. So they do! And it's defended with so much political firepower that the Republicans fail miserably and suffer massive casualties.
If this is how things work, it's a pretty awesome deal, and we should make sure it happens more often.