As Jacob Sullum noted below, the Supreme Court issued its long-awaited decision in McDonald v. Chicago this morning, ruling that the Second Amendment is incorporated against the states via the Due Process Clause of the 14th Amendment. This is a major victory for gun rights—as it opens the door for legal challenges to countless state and local gun control laws and finally gives the Second Amendment its due alongside the rest of the Bill of Rights—but it's not the victory it should have been. That's because only Justice Clarence Thomas followed the text and history of the Constitution and held that the Second Amendment must be incorporated via the Privileges or Immunities Clause of the 14th Amendment, not the Due Process Clause.
As Thomas notes in his concurrence,
the record makes plain that the Framers of the Privileges or Immunities Clause and the ratifying-era public understood—just as the Framers of the Second Amendment did—that the right to keep and bear arms was essential to the preservation of liberty. The record makes equally plain that they deemed this right necessary to include in the minimum baseline of federal rights that the Privileges or Immunities Clause established in the wake of the War over slavery. …
I agree with the Court that the Second Amendment is fully applicable to the States. I do so because the right to keep and bear arms is guaranteed by the Fourteenth Amendment as a privilege of American citizenship.
Note to libertarian history buffs: Thomas cites both Frederick Douglass and Lysander Spooner in his concurrence.