Andrew Koppelman pushes back against the idea that the Court could get away cleanly after overturning the mandate:

A decision invalidating the mandate would paint Obama into a corner, forcing him to make the Supreme Court a big issue in his reelection campaign. Bush v. Gore didn’t make the Court look good, but it didn’t lead to millions of dollars worth of television ads trying to persuade the American public that the Republicans on the Court are a bunch of despicable political hacks. Look what millions of dollars in negative ads have done to Mitt Romney’s poll numbers. Does the Court really want to subject itself to that?

Jon Walker thinks this sort of consideration would render a single-payer system safe – no matter how much the justices hate it as policy:

The Supreme Court has very little inherent democratic legitimacy. It’s legitimacy comes from it acting sparely and mostly with restraint. If the Court really did try something so blatant, it would run the real risk of being told by the President in Jacksonian style, "Roberts has made his decision, now let him enforce it." A true raw power showdown would not end well for the Court, and they should know that.