The Supreme Court considers the sex offender next door.

One thing you may be tempted to do, before you read this dispatch, is to go to your state's sex offender registry, and—if it's posted on the Internet—start randomly entering the names of every single person you know (21 states require at least some information about released sex offenders to be put on the Internet, and 16 others allow for but don't require it). I looked up the names of my Slate editors, neighbors, and friends in the Virginia sex offender registry today. And my husband. Let me tell you right now, Big Bird: When you've looked at the photos of the sexual offenders in your neighborhood, they may no longer be the people that you greet when you're walking down the street each day.

You'll probably hear several times on the news tonight that today's two cases, the first tests of the so-called "Megan's laws," is that these cases are about "balancing." The pundits will say that both the case challenging the Alaska sex offender registry and the one in Connecticut are about "weighing the rights of communities to protect themselves from dangerous recidivists against the right of individuals to be free from social stigma and isolation after they've served out their sentences."

Actually, that's not what today's cases were about. These cases are about how best to challenge a law on constitutional grounds. Or, more specifically, both cases are about how you can lose even the four most liberal justices on the Supreme Court by failing to state a compelling constitutional claim.

The various Megan's laws are named after 7-year-old Megan Kanka, who was raped and murdered in 1994 by a twice-convicted child sex offender who lived across the street from her in New Jersey. Outraged parents across the country felt that they had the reasonable right to know when a convicted child molester moved in next door, and as a result, all 50 states and the federal government passed slightly different versions of a law mandating that all convicted sex offenders register with their states, and in turn requiring the states to make that information widely available. Some states have enthusiastically embraced the widely available part of that law—with some using Internet registries, fliers, 900-numbers, and notices sent home in school children's backpacks.

The Alaska sex offender registry, passed in 1994, requires anyone convicted of sex offenses after 1984 to provide a name, address, place of employment, vehicle information, photographs, and fingerprints, and they must update that information every 90 days for life if convicted for a serious offense. They must provide updates annually for 15 years if convicted of a lesser offense. The offenders in question, John Does 1 and 2, argue that having committed their crimes and served their sentences before the law was enacted, they are being subject to an unconstitutional "ex post facto" law that criminally punishes conduct occurring before the law even existed. The 9^th Circuit Court of Appeals agreed.

The Connecticut registry was removed from the Internet after the 2^nd Circuit Court of Appeals ruled for another John Doe on a different constitutional theory. The Connecticut registry provides information similar to Alaska's, which is also updated regularly. In that case, the ex-sex-offender argued that by simply posting his name on a list of "dangerous" sex offenders without affording him an opportunity to prove he was no longer dangerous, Connecticut had imposed a stigma on him that violated his right to "procedural due process." In other words, he contends that you have a right to a hearing about your dangerousness before the state can go slapping you on a "sexual offender registry."

There are other constitutional challenges to the Megan's laws bubbling up through the lower courts, but these are the first two to reach the high court. Based on today's arguments, it's unlikely either the ex post facto or procedural due process claims will put an end to any Megan's law.

Justices John Paul Stevens and Antonin Scalia are late to work today, both likely delayed by the bridge and street closings connected to the capital's most recent bomb threat. What's most striking about this morning's argument is that each of the justices seems to have one principal concern about the various laws and repeats it over and over again.

In the Alaska case, Justice Anthony Kennedy points out at least eight times that "affirmatively" forcing someone to go to the police station four times a year, "presenting myself to a policeman," which is "degrading," is both burdensome and has "no analog" in the law. John Roberts, arguing in defense of the Alaska registry, responds that being burdensome does not make a law "punishment" (as opposed to mere civil regulation) for purposes of triggering the ex post facto rule.

Justice Ruth Bader Ginsburg's theme today will be that this law constitutes "punishment" because it doesn't tell "the whole truth" about the offenders. "There is no escape," she says. "We can prove with expert testimony that we're cured" but that information will not be posted. "They're locked into this for life." Roberts cites Kansas v. Hendricks, a 1997 Supreme Court ruling that upheld a state law requiring civil commitment for "sexually violent predators" finding that it was not a "punishment" in violation of the ex post facto clause. If locking someone up isn't punitive, asks Roberts, how can posting his name be?