Why go beyond the Constitution?

One very quick point on Alex’s argument (discussed by Peter in the post,”Translating citizenship outside the State”) that, in effect, “citizenship will move up the territorial chain.” I agree with Alex descriptively that new kinds of post-national citizenship would be established with new political entities, norms, coercive authority and the like. My problem is normative. It has not been explained how these new institutions can be democratic. Why would we want to go beyond the US Constitution for a new system of post-national governance that can not even be fully articulated?