The Supreme Court issued its decision in the McDonald gun case today, holding that the Second Amendment's protection of gun rights applies against state and local governments just as it applies to the federal government.
From a quick read of the decision, it appears to break down like this:
The majority opinion by Justice Alito holds that the Fourteenth Amendment's Due Process Clause "incorporates" the Second Amendment right to bear arms and therefore limits state and local governments just as it limits the federal government. Like Justice Scalia in the Heller decision two years ago, Alito is careful to reassure governments that the right to keep and bear arms is not “a right to keep and carry any weapon whatsoever in any manner whatsoever and for whatever purpose," so many gun-control laws will still stand.
Unsurprisingly, the majority opinion dismisses in a single paragraph the petitioners' argument that the 14th Amendment's Privileges or Immunities Clause, which the Supreme Court rendered toothless more than a century ago in the Slaughter-House Cases, protects gun rights. The Privileges or Immunities Clause is the provision in which some libertarians, such as Randy Barnett, put great hope for protection of liberty in the future — but the Supreme Court's decision here confirms that, however strong the legal arguments, the idea that the Supreme Court would ever do it is little more than wishful thinking.
Justice Scalia filed a concurring opinion in which he notes that he has trouble with the idea of "substantive due process" that the majority relies on (because it's nonsensical and not in the Constitution), but he nonetheless concurs in the result because if the Court is going to protect "fundamental" rights, then the right to bear arms surely counts as fundamental. He spends most of this opinion attacking a dissent by Justice Stevens because Stevens disregards the American tradition of respecting the right to bear arms and urges deference to legislators in defining what our rights are.
Justice Thomas filed a concurring opinion in which he argues that the Court should rely on the Privileges or Immunities Clause rather than the Due Process Clause in protecting fundamental rights. I'm not sure what "privileges or immunities" rightly include (and not sure that the question is really susceptible of a definitive answer), but I have no doubt that this would be a more reasonable ground for the decision. Unfortunately for supporters of this view, it is extremely unlikely that any Supreme Court justice other than Thomas will ever accept it.