I do not really understand why you expect the middle classes, and the 'middle way' in politics to be destroyed for sure. Since elcetions in the US seem to get pretty much perfect 50-50 outcomes, that suggest that politicians are very accurately aware of the median of (at least the voting part of) the public. I would suggest this gives the opinions of this middle class a very strong 'leverage': no matter what the more extreme wings think, if the middle groups shift their opinion slightly, this is immediately reflected in election outcomes, or changed party lines.

I can't help thinking that the median American voter is in fact not too unhappy with the current political situation, and that mild Republican ppolicies are exactly what they want. Even with the current Iraq backlash, political victory for the Democrats still seems far from certain, and the previous 'big shift' in Congress and Senate was, compared to the shifts in ordinary European elections, not that extreme at all.