The basis of Republican politicking was to "federalize" the process. And we ended up with issues which trivialized choices. Bedroom issues became more prevalent than foreign policy, for example. It worked as long as the electorate was terrified of the "bad guys," but after a while folks catch on.
Once the gang of corporatists, who believe advertising will always prevail, are left with nothing but the same jaded fear jingles, people take stock of their own situations. Republicans have nothing left to peddle.
What changes the milieu is talking to people (the 50 state model)where the political process begins to become less Washington oriented, and harder for candidates of either party to advertise as THE way. One evidence is that no current Democrat seeking the presidency turned up for the DLC conference in Nashville. It makes for interesting observations, like the new Hillary meeting the old Hillary. It's not the only observation, but one that caused "triangulation" to be put into perspective.
On the trail right now, we can observe all the examples on the Dem spectrum. Tweak the system, root out its big mistakes, reorient to domestic issues, etc. Thus the split even in the House. Radical to mainline comes up in bazaar ways, as in the Cindy versus Nancy episode. The Iraq debacle allows for the issue to surface, but I think it reaches much further into classic states rights issues. And that issue is still largely a cultural division between "melting pot" and "true American" feelings. This time immigration will be hotter than affirmative action, but the underlying scream is to find "the good ole days."
In my view, such groups as Blue Dogs appeal to the nostalgia crowd. The folks who promote the PDA approach are looking down the road. What road? Time will tell. The Democrats have the Speakership, and many are giving the Speaker hell. For once, I agree with Ronald Reagan. The Eleventh Commandment says to speak no evil of your party members. It's going to be very interesting to see whether those who campaign for House Democrats understand that federalizing national campaigns is what happened throughout the 20th Century until JFK bucked the system. Jack Kennedy's grandfather typified machine politics. We should be wary of setting up machines.