The U.S. Supreme Court case Puerto Rico v. Sanchez Valle, 2015, centered on the issue of whether Puerto Rico and the United States are separate sovereigns for purposes of the Double Jeopardy Clause - a constitutional protection that prevents an individual from being prosecuted twice for the same crime by two different jurisdictions. The defendants in this case were charged with selling firearms without a license in both federal and territorial courts. They argued that these prosecutions violated their double jeopardy rights as they were essentially being tried twice for the same offense. In a 6-2 decision, the Supreme Court ruled against Puerto Rico stating it is not a separate sovereign entity from U.S., hence cannot bring successive prosecutions after federal ones under Double Jeopardy Clause. The court reasoned that while Puerto Rico has significant autonomy to govern itself, its power ultimately comes from Congress which makes it less than fully independent or sovereign.

In the dissenting opinion for Puerto Rico v. Sanchez Valle, Justice Breyer, joined by Justice Sotomayor, argued that Puerto Rico should be considered a separate sovereign for purposes of the Double Jeopardy Clause. They contended that historical and practical factors demonstrated Puerto Rico's sovereignty. The justices pointed out that after 1952, when Congress approved Puerto Rico’s constitution giving it autonomy over its internal affairs including criminal law enforcement; this marked a significant change in the nature of its relationship with the United States and established it as an autonomous political entity. Therefore, they believed that prosecuting someone in both federal and local courts would not constitute double jeopardy because these are two different jurisdictions derived from distinct sources of power: one from U.S Congress (federal) and another from people of Puerto Rico (local). This view however was not shared by majority who held otherwise leading to their dissent.