Judicial Review
Article III (constitutional) federal courts in the Judicial Branch of government may declare a law unconstitutional under the doctrine of judicial review, but only if the law is relevant to a case or controversy before the court. The US Supreme Court is the final arbiter of constitutionality, however, and may overturn the lower courts' decision on appeal.
The only federal courts that have this power are:
Yes, a state court can declare a federal law or executive order unconstitutional if it is relevant to a lawsuit or other action before the court. However, the federal government would undoubtedly challenge that decision by appealing to the federal courts; the state courts cannot nullify a federal law. The US Supreme Court is the ultimate authority on constitutionality and would probably make the final decision.
The federal courts can check the Presidents power by that courts can declare executive actions unconstitutional.
"The federal courts can check the Presidents How_can_Federal_Court_check_the_presidents_powerby that courts can declare executive actions unconstitutional."
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If the President (representing the Executive Branch of government) signs a piece of legislation into law, the federal courts (representing the Judicial Branch of government) can find it unconstitutional - or - alter the unconstitutional aspects of it, in its application.
Judicial :)
Checks and balances
No, that is a power reserved for the courts of the Judicial Branch.
Any court can declare a law unconstitutional, but the government would appeal the decision to the US Supreme Court, the ultimate arbiter of constitutionality. Due to the appeals process, only the Supreme Court nullifies federal (and sometimes state) laws.
The Judicial Branch may declare laws related to cases before the courts unconstitutional.
It wouldn't be called null or void, but yes, the federal courts can and do declare a state and federal statutes unconstitutional. This has the effect of repealing the statute.
The courts have no power of enforcement; they can declare a statute unconstitutional and render it unenforceable, but they require the Executive Branch (President or Governor) to provide actual enforcement.
States from passing laws that contradict federal law.