In which case did the Supreme Court rule that a defense attorney is a constitutional right?

The ruling in Gideon v. Wainwright established the principle that the right to counsel is a constitutional right protected under the Sixth Amendment. This landmark case addressed the issue of whether states are required to provide legal counsel to defendants who cannot afford an attorney. The Supreme Court unanimously decided that the right to free legal counsel is essential for a fair trial, thus extending the right to defendants in state courts, not just federal courts. By ruling in favor of Gideon, the Court ensured that the fundamental fairness of the legal system is upheld, reinforcing the idea that access to legal representation is crucial for justice. This decision had a profound impact on the justice system, ultimately shaping the way defendants are treated in legal proceedings across the United States.

The other cases address different legal issues, such as self-incrimination in Miranda v. Arizona, racial segregation in public schools in Brown v. Board of Education, and the separation of church and state in Lemon v. Kurtzman, none of which pertain specifically to the right to counsel.