In Blanco v. Hubbard, the United States Supreme Court in 1910 examined whether a Puerto Rican court had jurisdiction over an American citizen living in Puerto Rico who was accused of committing fraud in Cuba. The defendant, Mr. Blanco, argued that he could not be extradited to Cuba because the extradition treaty between the U.S and Spain did not apply to him as it predated America's acquisition of Puerto Rico following the Spanish-American War. However, this argument was rejected by both lower courts and eventually by the Supreme Court itself which held that treaties signed by nations continue to remain valid even after territorial changes unless explicitly annulled or modified. Therefore, since no such modification had been made regarding this particular treaty with Spain at that time, it continued to apply within newly acquired territories like Puerto Rico as well.

In the dissenting opinion for Blanco v. Hubbard, Justice Harlan argued that the majority's decision was inconsistent with previous rulings and principles of constitutional law. He contended that Puerto Rico should be considered a territory incorporated into the United States after its acquisition following the Spanish-American War, thus making it subject to all provisions of the U.S Constitution. Therefore, he disagreed with the majority's view that double jeopardy protections did not apply in this case because they were not "fundamental" rights extended to unincorporated territories like Puerto Rico under their interpretation of Downes v. Bidwell (1901). In his view, such an interpretation undermined basic individual liberties protected by our constitution and set a dangerous precedent for future cases involving territorial jurisdictions.