Porter v. United States was a Supreme Court case that addressed the issue of whether a defendant could be convicted of a crime if the evidence presented was obtained through an illegal search and seizure. The case involved a man named Porter who was accused of stealing a horse. The police searched Porter's home without a warrant and found evidence of the crime. Porter argued that the evidence should not be used against him because it was obtained through an illegal search and seizure. The Supreme Court ruled in favor of Porter, holding that evidence obtained through an illegal search and seizure could not be used against a defendant in a criminal trial. The Court reasoned that the Fourth Amendment of the Constitution protects citizens from unreasonable searches and seizures, and that the evidence obtained in this case was obtained in violation of that amendment. The Court also noted that the exclusionary rule, which prohibits the use of illegally obtained evidence in criminal trials, was necessary to protect citizens from unreasonable searches and seizures. The Porter v. United States decision established an important precedent in criminal law, as it established the exclusionary rule and made it clear that evidence obtained through an illegal search and seizure could not be used against a defendant in a criminal trial. This decision has been cited in numerous cases since then, and it remains an important part of criminal law today.

In Porter v. United States, the Supreme Court was asked to decide whether a defendant could be convicted of two separate offenses for one act that violated both state and federal law. The majority opinion held that such convictions were permissible under the dual sovereignty doctrine, which allows states and the federal government to prosecute individuals for violating their respective laws without infringing on each other's authority. Justice Field dissented from this decision, arguing that allowing multiple prosecutions would lead to double jeopardy in violation of constitutional protections against it. He argued further that Congress had not intended its legislation to permit such an interpretation when it passed those laws; rather, he believed they should only apply once per offense regardless of jurisdiction or level of government involved. Ultimately, his dissent failed as the majority opinion prevailed in this case