Under what authority do states regulate criminal law?

• A. The 8th Amendment
• B. The First Amendment
• C. The 14th Amendment
• D. The 10th Amendment

Answer: (D)

The authority comes from the Tenth Amendment, which reserves powers not delegated to the United States to the states or the people. This is why states regulate most criminal law: they exercise their police power to maintain public safety and order within their borders. The federal government handles crimes that implicate federal interests or cross state lines, but the day‑to‑day definition of crimes and criminal procedure is a state function. The Fourteenth Amendment binds states to constitutional protections in criminal cases, but it does not grant them general power to regulate criminal law. The Eighth and First Amendments address limits on punishment and protections of rights, not the source of state criminal authority.