Today the Supreme Court ruled that Chicago's handgun ban violates the right to keep and bear arms. The 5-to-4 decision confirms that the Second Amendment binds state and local governments as well as federal domains such as the District of Columbia, which had a similar gun law that the Court overturned in the landmark 2008 case D.C. v. Heller. The Court ruled that the Second Amendment, like most other protections in the Bill of Rights, applies to the states by way of the 14th Amendment's Due Process Clause. It rejected an invitation to revive the amendment's Privileges or Immunities Clause, a more plausible basis for incorporation.
Addendum: Regarding the appropriate route for incorporation, Justice Antonin Scalia, an outspoken critic of substantive due process, has this to say in his concurring opinion:
Despite my misgivings about Substantive Due Process as an original matter, I have acquiesced in the Court's incorporation of certain guarantees in the Bill of Rights "because it is both long established and narrowly limited." This case does not require me to reconsider that view, since straightforward application of settled doctrine suffices to decide it.
In his concurring opinion, by contrast, Justice Clarence Thomas makes the case for enforcing the Privileges or Immunities Clause:
Applying what is now a well-settled test, the plurality opinion concludes that the right to keep and bear arms applies to the States through the Fourteenth Amendment's Due Process Clause because it is "fundamental" to the American "scheme of ordered liberty"...and "'deeply rooted in this Nation's history and tradition.'"...I agree with that description of the right. But I cannot agree that it is enforceable against the States through a clause that speaks only to "process." Instead, the right to keep and bear arms is a privilege of American citizenship that applies to the States through the Fourteenth Amendment's Privileges or Immunities Clause....
This Court's substantive due process framework fails to account for both the text of the Fourteenth Amendment and the history that led to its adoption, filling that gap with a jurisprudence devoid of a guiding principle. I believe the original meaning of the Fourteenth Amendment offers a superior alternative, and that a return to that meaning would allow this Court to enforce the rights the Fourteenth Amendment is designed to protect with greater clarity and predictability than the substantive due process framework has so far managed.