From Chief Justice John Roberts' majority opinion upholding the Affordable Care Act:

We do not consider whether the Act embodies sound policies. That judgment is entrusted to the Nation’s elected leaders. We ask only whether Congress has the power under the Constitution to enact the challenged provisions. ...

In this case we must again determine whether the Constitution grants Congress powers it now asserts, but which many States and individuals believe it does not possess. Resolv- ing this controversy requires us to examine both the limits of the Government’s power, and our own limited role in policing those boundaries.