June 27 (Bloomberg) -- The U.S. Supreme Court ended its term with a clear reminder: Justice Anthony Kennedy is in charge.

In the past three weeks, Kennedy made the difference in 5-4 decisions covering Guantanamo Bay inmates, the death penalty for child rape and campaign-finance rules. Yesterday, on the term's final day, he again provided the fifth vote as the court said the Constitution's Second Amendment protects an individual's right to own a gun.

With the court splitting along ideological lines, only Kennedy, 71, was in the majority in all four of those cases.

``Anyone who can count can see that he is critical,'' said A.E. Dick Howard, a constitutional law professor at the University of Virginia in Charlottesville.

The gun ruling struck down the District of Columbia's handgun ban and may lead to challenges over weapons restrictions elsewhere. The ruling resolved a constitutional question that lurked for two centuries: whether the Second Amendment covers people who aren't affiliated with a state-run militia.

``The enshrinement of constitutional rights necessarily takes certain policy choices off the table,'' Justice Antonin Scalia wrote for the majority. ``These include the absolute prohibition of handguns held and used for self-defense in the home.''

Ideological Split

The justices divided along lines that have repeatedly split the court under Chief Justice John Roberts. Kennedy, Roberts and Justices Clarence Thomas and Samuel Alito joined Scalia's opinion. Justices John Paul Stevens, Stephen Breyer, Ruth Bader Ginsburg and David Souter dissented.

``The right the court announces was not `enshrined' in the Second Amendment by the framers,'' Stevens wrote. ``It is the product of today's law-changing decision.''

Scalia said government can still bar handgun possession by convicted felons and the mentally ill, and restrict bringing guns into schools or government buildings. He also suggested that concealed-weapons bans were constitutional.

Still, the decision may make gun restrictions in Chicago, New York City and other cities more vulnerable to legal challenges. Gun rights advocates including the National Rifle Association vowed to begin new legal moves and said some background checks and automatic-weapon bans are legally questionable.

The justices today turned away an appeal from a man who said the Second Amendment required reversal of his conviction for violating the former federal ban on some semiautomatic assault weapons. The law expired in 2004.

The validity of restrictions may depend on Kennedy, Howard said. Kennedy ``may take a fairly generous view of state police power and vote with the four liberals to uphold regulations,'' he said.

Strictest Ban

Washington's 32-year-old gun law, perhaps the strictest in the nation, barred most residents from owning handguns and required that all legal firearms be kept unloaded and either disassembled or under trigger lock. Six residents disputed the law, saying they wanted firearms at home for self-defense.

``After 30 years of ignoring that right, the District will finally have to respect it,'' said one of the residents, Dick Heller, who works as an armed security guard at a federal government building in Washington.

Washington's mayor, Adrian Fenty, said he is disappointed. ``More handguns in the District will mean more gun violence,'' he said at a press conference.

The decision didn't resolve whether the Second Amendment binds the states in addition to the federal government and the nation's capital.

Second Amendment

Adopted in 1791 as part of the Bill of Rights, the Second Amendment reads: ``A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed.''

The justices in the majority said they had ``no doubt, on the basis of both text and history, that the Second Amendment conferred an individual right to keep and bear arms.''

The Supreme Court hadn't considered the Second Amendment since 1939, when it issued a ruling that both sides in the debate later claimed as support for their arguments.

The ruling drew words of support from both major-party presidential candidates. Republican John McCain in a statement called gun ownership a ``fundamental right -- sacred, just as the right to free speech and assembly.''

Democrat Barack Obama said on Bloomberg Television that he agrees with the court's ``overall reasoning'' and the Washington gun ban probably ``overshot the runway.''

Kennedy's Views

Kennedy's views on the gun case became clear during arguments in March, when he said the Second Amendment confers ``a general right to bear arms quite without reference to the militia either way.'' After the arguments, proponents of the ban conceded they almost certainly would lose on the individual-rights question.

Kennedy wrote the court's majority opinions on Guantanamo Bay and child rape, joining the liberal bloc in those rulings. In the Guantanamo case, he said the inmates have constitutional rights and can seek release in federal court.

``The laws and Constitution are designed to survive, and remain in force, in extraordinary times,'' he wrote.

In the rape case, Kennedy said execution was a disproportionate penalty for a crime that didn't take the victim's life. He provided the fifth vote for the campaign- finance ruling, which struck down a law that made it easier for opponents of wealthy U.S. House candidates to raise money.

``He's beginning to flex his muscles,'' Howard said. ``His opinion style is a bit more self-confident, a bit more expansive, as if he's looking not only to the opinion at hand but also the history books.''

To contact the reporter on this story: Greg Stohr in Washington at gstohr@bloomberg.net.

Last Updated: June 27, 2008 10:24 EDT