A recent comment inspired me to wonder whether the US federal government has the power to directly modify state law.
State legislatures will often pass bills of the form "Section so-and-so of the North Wherever General Statutes is ammended to read: blah".
If Congress passed and the President signed a federal bill of the same form, would the statutes of the named state actually change?
Can the federal government directly modify state law?
No.
The U.S. Supreme Court has limited the authority of Congress to directly regulate the operations of state governments. This is called the anti-commandeering doctrine.
It is articulated in U.S. Supreme Court cases like New York v. United States, 505 U.S. 144 (1992), which held that the Low-Level Radioactive Waste Policy Amendments Act of 1985, which, among other things, imposed upon states the obligation to provide for the disposal of waste generated within their borders, unconstitutionally commandeered states to enact legislation that the federal government directed it to enact.
Congress can pass federal laws that pre-empt, which is to say, nullify or invalidate, state and local laws, and it can give states an incentive to modify state laws, but it cannot actually modify state laws directly, itself.
The U.S. government can also directly modify the laws of the District of Columbia, Puerto Rico, or other self-governing territories because all of them are not part of U.S. states. This authority over areas outside of U.S. states which is granted to Congress under Section 8 of Article I to the U.S. Constitution, and is limited primarily by Section 2 of the Twenty-First Amendment, which arguably forbids Congress from modifying the the alcohol laws and regulations of these self-governing possessions of the United States which are not parts of U.S. states.
Congress very frequently amends federal laws. This recently-enacted law by saying:
Section 2002(a)(4) of the Johnny Isakson and David P. Roe, M.D. Veterans Health Care and Benefits Improvement Act of 2020 (Public Law 116–315; 38 U.S.C. 5101 note) is amended by striking ‘‘three years’’ and inserting ‘‘five years’’
Congress is limited to re-writing acts previously enacted by Congress. It cannot rewrite a state law. It also cannot rewrite a federal regulation, which is written by the executive branch. What it can do is rewrite an act of Congress that was the statutory underpinning of a federal regulation, which normally results in the executive branch rewriting some regulation (in a manner consistent with what Congress wrote).
Congress might pass a law that has the indirect effect of inspiring a state to rewrite one of its law, for example a new law might put stronger conditions on federal funding, which could inspire a state to modify some law regarding college funding or highway operation. There can be constitutional issues related to state power vs. federal preemption whereby Congress cannot enact a law that compels states to enact a certain law, as in aspects of Obamacare as decided in NFIB v. Sebelius.
