For the first time in the nation's history, the Supreme Court recognized today that the Second Amendment gives individuals the right to keep a gun at home for protection.
The court struck down Washington, D.C.'s ban on handguns as well as a provision requiring long guns to be stored with a trigger lock.
The 5-4 ruling will reshape the debate over gun control, which has long been heatedly debated in Congress. That the outcome was decided by a single justice will help thrust the issue of future Supreme Court appointments into the middle of the presidential race.
Senator McCain, the presumptive Republican nominee, issued a statement calling the decision a "landmark victory," and praising the Supreme Court for recognizing that "gun ownership is a fundamental right - sacred, just as the right to free speech and assembly."
Senator Obama, the presumptive Democratic nominee for president and a former law professor, was more tepid, saying "I have always believed that the Second Amendment protects the right of individuals to bear arms."
Washington's handgun ban was considered the most restrictive in the nation, with Chicago's ban a close second. The next legal fight over handgun regulation may well focus on Chicago, the city which Mr. Obama calls home.
In his statement, Mr. Obama seemed to suggest that he supported that handgun ban there. Referring to gun regulation, he said: "I know that what works in Chicago may not work in Cheyenne."
Justice Scalia was joined by Chief Justice Roberts and Justices Thomas, Kennedy, and Alito. The dissenters were Justices Ginsburg, Souter, Breyer, and Stevens.
"The American people have considered the handgun to be the quintessential self-defense weapon," Justice Scalia wrote for the majority, in explaining why it was not enough for the Second Amendment to protect private ownership of rifles and shotguns, but not handguns.
The decision, while a symbolic victory for the tens of millions of Americans who own guns, gives few hints about whether any gun regulation beyond Washington's ban is unconstitutional.
"Like most rights, the right secured by the Second Amendment is not unlimited," Justice Scalia wrote. "Nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms,"
Justice Scalia also seemed to express some ambivalence about encouraging gun ownership as a policy matter.
"Undoubtedly some think that the Second Amendment is outmoded in a society where our standing army is the pride of our Nation, where well-trained police forces provide personal security, and where gun violence is a serious problem," Justice Scalia wrote. "That is perhaps debatable, but what is not debatable is that it is not the role of this Court to pronounce the Second Amendment extinct."
In a dissent, Justice Stevens espoused a different view of the Second Amendment. He argued that its aim was not to "enshrine the common-law right of self-defense in the Constitution," but to "protect the right of the people of each of the several States to maintain a well-regulated militia."
Justice Stevens voiced concern about the prospect that the decision would unsettle existing gun control laws.
"Until today, it has been understood that legislatures may regulate the civilian use and misuse of firearms so long as they do not interfere with the preservation of a well-regulated militia," Justice Stevens wrote. "The Court's announcement of a new constitutional right to own and use firearms for private purposes upsets that settled understanding."
He continued later, "I fear that the District's policy choice may well be just the first of an unknown number of dominoes to be knocked off the table."