"New Jersey won a landmark ruling from the Supreme Court Monday that could lead many states to legalize betting on college and professional sports."

USA Today reports.

The justices ruled 7-2 that a 25-year-old federal law that has effectively prohibited sports betting outside Nevada by forcing states to keep prohibitions on the books is unconstitutional... Justice Samuel Alito, a New Jersey native, wrote the court's opinion in the case. Justices Ruth Bader Ginsburg and Sonia Sotomayor dissented....

"Congress can regulate sports gambling directly, but if it elects not to do so, each state is free to act on its own," Alito said. "Our job is to interpret the law Congress has enacted and decide whether it is consistent with the Constitution. [The Professional and Amateur Sports Protection Act] is not."...

During oral argument in December, several conservative justices said the law impermissibly "commandeered" states to keep their bans on the books. But several liberal justices said Congress merely pre-empted state laws, a commonplace action.

What has made the law anachronistic is the advent and rapid growth of Internet gambling. Rather than stopping sports betting, it helped push more of it underground, creating a $150 billion annual industry.....

Here's the opinion (PDF). Excerpt:

The PASPA provision at issue here—prohibiting state authorization of sports gambling—violates the anticom­mandeering rule. That provision unequivocally dictates what a state legislature may and may not do. And this is true under either our interpretation or that advocated by respondents and the United States. In either event, state legislatures are put under the direct control of Congress. It is as if federal officers were installed in state legislative chambers and were armed with the authority to stop legislators from voting on any offending proposals. A more direct affront to state sovereignty is not easy to imagine.

Neither respondents nor the United States contends that Congress can compel a State to enact legislation, but they say that prohibiting a State from enacting new laws is another matter. See Brief for Respondents 19; Brief for United States 12. Noting that the laws challenged in New York and Printz “told states what they must do instead of what they must not do,” respondents contend that com­mandeering occurs “only when Congress goes beyond precluding state action and affirmatively commands it.” Brief for Respondents 19 (emphasis deleted).

This distinction is empty. It was a matter of happen­ stance that the laws challenged in New York and Printz commanded “affirmative” action as opposed to imposing a prohibition. The basic principle—that Congress cannot issue direct orders to state legislatures—applies in either event.

Here is an illustration. PASPA includes an exemption for States that permitted sports betting at the time of enactment, §3704, but suppose Congress did not adopt such an exemption. Suppose Congress ordered States with legalized sports betting to take the affirmative step of criminalizing that activity and ordered the remaining States to retain their laws prohibiting sports betting. There is no good reason why the former would intrude more deeply on state sovereignty than the latter....

The legalization of sports gambling requires an im­portant policy choice, but the choice is not ours to make. Congress can regulate sports gambling directly, but if it elects not to do so, each State is free to act on its own. Our job is to interpret the law Congress has enacted and decide whether it is consistent with the Constitution. PASPA is not. PASPA “regulate[s] state governments’ regulation” of their citizens, New York, 505 U. S., at 166. The Constitu­tion gives Congress no such power.