Democrats and Republicans are still the two main parties. Religious Social issues are no longer a major factor in campaigns, instead economic and foreign relation topics dominate political dialog. One of the parties is isolationist/protectionist (I'm guessing the Republicans) and the other supports free trade and greater involvement in world politics.
With the ways trends are going I'd say it would be the other way around. I'll say it again the Republicans will be a much more liberterian although socially conversative party and the Democrats will be a much more Social Democratic then liberal party overall.
