9. According to the doctrine of preemption , which statements is true? The Senate must act before the House to override a presidential veto. The president may withdraw legislation before Congress considers it. Congress can ask the Supreme Court to remove local governments. State constitutions and statutes may not contradict federal law.

The doctrine of preemption is a legal principle that holds that certain federal laws take precedence over state laws. This means that if a federal law and a state law conflict, the federal law must be followed. The doctrine is based on the Supremacy Clause of the U.S. Constitution, which establishes that federal law is the "supreme law of the land." Therefore, state constitutions and statutes may not contradict federal law. The other options provided do not relate to the doctrine of preemption.