WASHINGTON — The U.S. Supreme Court ruled on some of the country’s most divisive issues in its just-completed term. The court may have also injected itself into the presidential campaign.

The justices ended their nine-month term with a flurry of decisions on Guantanamo Bay inmates, the death penalty, the Exxon Valdez oil spill, campaign finance, and gun rights.

The rulings underscored how the next president might reshape the court through new appointments. Each case was decided by a single vote and, almost without exception, pitted the justices praised by Senator McCain, a Republican, against those preferred by Senator Obama, a Democrat. Mr. McCain sought to use the decisions to distinguish himself from his rival.

“This is going to come back over and over again between now and November,” the editor of the non- partisan Rothenberg Political Report, Stuart Rothenberg, said. “Both sides will be going to the well again, saying, ‘You want to know why this election is crucial? This is it.'”

The balance may shift in coming years, particularly if Mr. McCain wins and can nominate a conservative to replace a liberal — possibly John Paul Stevens, 88, or Ruth Bader Ginsburg, 75. With six justices over age 68, the next president may get several appointments.

The Guantanamo ruling drew the strongest candidate reactions. Voting 5-4, the justices said the 270 inmates held at the American naval base in Cuba have constitutional rights and may seek release in federal court.

The majority included the three justices whom Mr. Obama said in May would be models for his nominations — Ginsburg, Stephen Breyer, and David Souter — along with Justice Stevens and a swing vote, Anthony Kennedy.

On the other side were the men Mr. McCain has touted as his prototypes: Chief Justice John Roberts and Justice Samuel Alito, who joined justices Antonin Scalia and Clarence Thomas in dissent.

Mr. Obama, 46, an Illinois senator, praised the decision as “a rejection of the Bush administration’s attempt to create a legal black hole at Guantanamo.” Mr. McCain, 71, an Arizona senator, called the ruling “one of the worst decisions in the history of this country.”

The identical lineup produced a 5-4 ruling barring the death penalty for child rape. Similar splits took place in the Valdez, gun, and campaign finance cases, though those fights produced conservative victories.

In the Valdez ruling, which cut $2 billion from the damages award against Exxon Mobil Corp. for the 1989 Alaskan spill, justice Souter and Kennedy joined the conservatives to produce a 5-3 decision. Justice Alito didn’t participate because he owns Exxon stock.

The gun and campaign-finance rulings were 5-4, as Justice Kennedy joined the four conservatives. In the campaign case, the court invalidated a federal law that made it easier for opponents of wealthy U.S. House candidates to raise money.

The gun ruling declared that the Constitution’s Second Amendment protects an individual right to bear arms and struck down a District of Columbia handgun ban.

The decision ensured that the court will be evaluating the legality of other weapons restrictions for years to come. The political impact nonetheless would have been greater had the case come out the other way, one of the city’s attorneys, Tom Goldstein of Akin Gump in Washington, said.