When liberal defense of federal power to govern results in a criminal conviction being upheld

I've just added a somewhat different version of the paragraphs below to my earlier post in which I'm compiling a list of the Supreme Court cases of the last term in which law school clinics participated in the litigation -- but the case has its own independent interest, for the way that a liberal defense of a broad understanding of federal power led to an affirmance of a troubling instance of the modern regime of sex offender registration statutes.

The case was United States v. Kebodeaux (No. 12-418, decided June 24, 2013). Kebodeaux, who in 1999 "had consensual sex with a 15-year-old girl when he was a 20-year-old Airman in the U.S. Air Force," as Justice Thomas writes in his dissent, was court-martialed, convicted, and served three months in prison. He also received a bad-conduct discharge, and on his return to civilian life became subject to sexual offender registration requirements in a federal statute called the Wetterling Act. Subsequently Congress replaced those requirements with new and in some respects tighter ones, in the Sex Offender Registration and Notification Act (SORNA), passed in 2006. After moving from one Texas city to another, Kebodeaux didn't update his sex offender registration as SORNA required (that is, within three business days of his move), and as a result he was convicted of the crime of failure to comply with the SORNA requirement, a felony, and sentenced to a year and a day in prison. 

There are many things one might want to argue to challenge this conviction. (In the Supreme Court, the Northwestern University Supreme Court Practicum helped represent Kebodeaux, and that's why I've listed it in the earlier post.) As the Supreme Court majority viewed the case, however, it did not feature any challenge based on the argument that Kebodeaux's punishment for violating a statute passed long after his crime and conviction was invalid under either the ex post facto or the due process clauses of the constitution. Instead, the sole issue the Court addressed (though Justice Thomas spoke about more) was whether Congress had any affirmative power to subject Kebodeaux to SORNA at all. That is, the issue before the Court was about the extent of Congress' powers in the first place, not the limits on those powers that constitutional rights might establish. Since obviously no provision of the Constitution expressly authorizes Congress to pass sex offender registration laws, the case was a test of the meaning of the "Necessary and Proper" clause, which enables Congress to pass any laws necessary and proper to carrying out any of the powers of any branch of the federal government. 

As a result, this case became a site of battle over the breadth of federal powers. Four of the conservative justices in one way or another made clear that they were opposed to too broad an understanding of the Necessary and Proper clause (though two of them, Roberts and Alito, found narrower rationales on which to affirm this particular statute's validity). Only Justice Kennedy, among the conservatives, joined in the majority decision, written by Justice Breyer and also joined by Justices Ginsburg, Sotomayor and Kagan -- in short, by the Court's liberal justices. Thus it was primarily the liberals, who might have been expected to find Kebodeaux's situation disturbing, who instead found themselves defending the concept of broad congressional "Necessary and Proper" authority and in the process affirming Kebodeaux's conviction for violating the federal sex offender registration statute. 

I'm pretty sure that qualifies as ironic!