Final answer:
The Supreme Court uses judicial review to declare laws and presidential actions unconstitutional.
Step-by-step explanation:
The process that the Supreme Court uses to declare laws and presidential actions unconstitutional is judicial review. This is the power of the court to review the constitutionality of laws and government actions. Through judicial review, the Supreme Court can strike down laws and actions that it deems to be in violation of the Constitution.
Learn more about Judicial Review