Like the European Council of the E.U., the U.S. Senate has polities rather than citizens as represented members. That is
to say, in both cases, the states are represented. In the case of the E.U., the
chief executives of the respective states represent them. In the U.S. case, the
citizens of the states elect senators directly, who in turn are tasked with
representing their respective states.
From the standpoint of representing the polities, the E.U. case is tighter, for
a U.S. senator is susceptible to the temptation to vote in the interests of the
state’s citizens who voted rather than of the state itself. The two interests
may overlap, but they are not identical, for citizens of a member-state may or
may not be interested in protecting the prerogatives of the state (government).
The Republican legislative responses to the Affordable Care Act (i.e., “Obamacare”)
are a case in point.
The full essay is at "U.S. Senators Falling Short."
For more on the U.S. Senate and the E.U. Council, see the book: Essays on Two Federal Empires, available in print and as an ebook at Amazon.com.