I think this may be a little different. There is a sizable minority on the left that is rabid about getting the US out of Iraq. Assume for a second that there is no change in the next two years. How is this group going to react to the democrats returning to the well for their support? Assume four years of no change. Assume six years. The point of course is that given enough time, this will certainly be as destructive to the democrats as the growth in government is to the republicans.

Both parties are made up of groups who would not necessarily align, but do so because they get their political itches scratched better in one party than the other. 45 years ago, both parties were "tough" on national security. Within 10 years the democrats had markedly move away from the "tough" position. I think as much or more than race issues, this is what split the south off from the democratic party (and the north east/coastal west off of the republican party). But when one of the groups in the political party doesn't get their political itch scratched and the other party is in no position to make a claim to scratch that itch, things get interesting. Some will stay in the party because its the lesser of two evils. Others will drop out of the political process. And the entire group becomes ripe for a third party candidate.