Can a president be indicted by State law but not by Federal law?

[The Velveteen Ocelot]

14. It's not clear. The Supremacy Clause of the Constitution says:

"This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding." This is the basis of the doctrine of federal preemption, which means that a federal law will always prevail over a contrary state law, and applies regardless of whether the conflicting laws come from legislatures, courts, administrative agencies or constitutions.

The DoJ has taken the position twice that the president is not subject to indictment while in office and that no criminal charges can proceed against him unless he's either removed from office by impeachment or has served out his term. This is just a policy position based on Office of Legal Counsel memoranda written during the Watergate scandal and again in 2000, so it's not really a law. It's still unresolved whether a sitting president can be indicted.

However, if the Supreme Court were to rule that the indictment of a president is unconstitutional under separation of powers or other theories, that decision would prevail over all indictments, including those arising in state courts.