It was just a rebuilding period. Political parties are like brands and eventually your brand becomes stale and old fashioned. People can't easily define you and instantly know what you're about, so a competing brand takes your place.
It's like the coke and pepsi wars. Both are old, established brands that constantly compete with eachother. They each have a loyal base but compete for those consumers in the middle who could buy either one. Coke and Pepsi both take turns winning over these folks for certain periods of time through things like exciting new products or catchy advertising.
The Democrats were just in their "new coke" phase in the 80s.
This.
Though it will be very interesting to see what happens in the next few years. On one hand, it seems that Republicans have enough small Southern and Rural states and congressional districts to hold to do very well in Congress but Democrats seem to have enough Urban and Suburban states to be at a good advantage for Presidential races. I think, if anything, the next two cycles will determine whether Democrats campaign as a hard liberal party or social liberal party in the not too distant future. I don't think they will try to go back to try to win back traditional blue dogs if they won't even vote for Pryor or Landrieu.
