The bottom line in the Health Care Cases (National Federation of Independent Business v. Sibelius) is to uphold the ACA while simultaneously creating a judicially imposed limit on the power of Congress to withold federal funds from the states. One reading of this result is that it is an unqualified victory for the Obama Administration and signals that Justice Roberts has assumed a new role as a "moderate"--situating him to the left of Justice Kennedy and at the center of the Court. In my view, that reading is quite implausible. First, Justice Roberts opinion on the Commerce Clause issue endorses the so-called new federalist understanding of the Congress's Article I powers. Roberts strongly endorses categorical limits on the commerce clause, and explicitly adopts the theory that the word "proper" in the Necessary and Proper clause creates independent, judicially-enforceable limits on the Congress when it relies on the sweepings clause. Second, Roberts opinion is the first in the modern era to suggest that the spending power is subject to judicially enforceable limits: the new-federalist camels nose is in the one tent where the notion of pleanary and unlimited power still seemed relatively secure. Third, and much more speculatively, Roberts upholds the mandate on the theory that it is a tax; that characterization may or may not "stick" on the wall of public opinion, but if it does, it will not be favorable to the President. Fourth, he accomplishes all of this while avoiding the worst scenarios for the institutional authority and legitimacy of the Court: the decision gives the left no room for a serious attack, while giving enough to the right to avoid substantial problems from that side of the aisle.
Although this post expresses my own views and any defects are solely mine, I must acknowledge Howard Gillman for inspiring much of its substance in an online mail-list post.