United States v. Watson was a Supreme Court case decided in 1976. The case involved a challenge to the constitutionality of a federal statute that allowed for warrantless arrests of persons suspected of committing felonies. The defendant, Watson, was arrested without a warrant for a felony he was suspected of committing. He argued that the statute was unconstitutional because it violated the Fourth Amendment's protection against unreasonable searches and seizures. The Supreme Court held that the statute was constitutional. The Court reasoned that the statute was a reasonable exercise of Congress' power to protect the public from dangerous criminals. The Court noted that the statute was narrowly tailored to only allow for warrantless arrests in cases where there was probable cause to believe that a felony had been committed. The Court also noted that the statute provided safeguards to protect the rights of the accused, such as requiring that the arresting officer have probable cause and that the arrest be made in a reasonable manner. In conclusion, the Supreme Court held that the statute was constitutional and that Watson's arrest was valid. The Court's decision established that warrantless arrests of persons suspected of committing felonies are permissible under certain circumstances.

In the dissenting opinion of United States v. Watson, Justice Brennan argued that the majority’s decision to uphold a warrantless search of an individual’s home was unconstitutional and violated the Fourth Amendment. He noted that while there may be some exceptions to the requirement for a warrant in certain cases, this case did not meet any such exception as it involved no exigent circumstances or other special considerations. Furthermore, he argued that allowing police officers to conduct searches without warrants would lead to arbitrary and unreasonable intrusions into people's homes which is precisely what the Fourth Amendment sought to prevent. In conclusion, Justice Brennan believed that upholding this type of search would set a dangerous precedent by eroding citizens' rights under the Constitution and should therefore be overturned on appeal.