The Supreme Court on Wednesday raised doubts about whether Puerto Rico should be treated as a sovereign state with powers that go beyond its status as a territory of the United States.
The justices considered the question during arguments in a criminal case involving two men who claim that Puerto Rico and the federal government can't prosecute them for the same charges of selling weapons without a permit.
The double jeopardy principal prevents defendants from being tried twice for the same offense. But there is an exception that allows prosecution under similar state and federal laws, since states are considered separate sovereigns.
Several justices said Puerto Rico's power to enforce local laws really comes from Congress, which in theory could take it away.
The case has broad political and legal implications that could affect Puerto Rico on issues ranging from taxation and bankruptcy to federal benefits. It comes as the high court prepares to hear a separate dispute later this year over whether the financially struggling Puerto Rican government can give its municipalities the power to declare bankruptcy.
The Caribbean island of 3.5 million people is a U.S. territory acquired in 1898 following the Spanish-American War. But it gained a measure of autonomy in 1952, when it adopted its own constitution with the approval of Congress and was allowed to pass its own local laws.
Justice Elena Kagan said that history means the ultimate source of the island's legal power is Congress.
"If Congress is in the driver's seat, why isn't Congress the sole source of authority?" she asked Christopher Landau, the lawyer representing Puerto Rico.
Landau said that under Puerto Rico's constitution "the political power of the commonwealth emanates from the people." He said Congress had essentially relinquished control over Puerto Rico's internal affairs when it allowed the island to create its own laws and government.
But Justice Antonin Scalia said that doesn't mean Congress couldn't change the law.
Justice Sonia Sotomayor, the daughter of Puerto Rico-born parents, seemed sympathetic to the argument that Congress meant to confer sovereignty when it approved the island's constitution — even if Puerto Rico is not quite equivalent to a state.
"Before 1952, Congress could veto Puerto Rico's laws," Sotomayor said. "It has relinquished that right."
The case involves Luis Sanchez Valle and James Gomez Vazquez, who pleaded guilty in federal court to selling illegal firearms. When Puerto Rican officials later charged them under local laws, they moved to dismiss the charges on double jeopardy grounds.
The Puerto Rico Supreme Court ultimately sided with the men, ruling that the island is not a separate sovereign.
Arguing for Valle and Vazquez, lawyer Adam Unikowski said the issue is simple: "States are sovereign, territories are not."
Some justices appeared to search for a middle ground. Justice Stephen Breyer said an opinion saying Puerto Rico is sovereign would have "enormous implications." But he suggested the court could find that the island has some aspects of sovereignty that would apply more narrowly to double jeopardy.
"There are different kinds of territories," Breyer said.
The Obama administration has angered Puerto Rican officials by insisting that the island remains a territory subject to the control of Congress.
Justice Department lawyer Nicole Saharsky told the justices that Congress has allowed "increasing self-government" in Puerto Rico and there is no reason to think lawmakers change that. But she said Congress could revise the arrangement because the island remains a territory.
"Congress is the one who makes the rules," Saharsky said.