Martial law can be legal, but only when justified.
But Biden did NOT authorize martial law.
{...
An updated U.S. Department of Defense (DOD) directive does not authorize federal troops to use lethal force against citizens, contrary to social media posts misrepresenting the revision ahead of the 2024 U.S. presidential election.
Under the
Posse Comitatus Act, opens new tab, it is illegal for military personnel to use force against people in the United States, unless for self-defense where authorized by Congress.
...
DOD Directive 5240.01, opens new tab was reissued on Sept. 27 as a routine measure to clarify approval authorities for intelligence activities, Gough said in an email.
“The policies concerning the use of force by DOD addressed in DoDD 5240.01 are not new, and do not authorize the DOD to use lethal force against U.S. citizens or people located inside the United States, contrary to rumors and rhetoric circulating on social media,” she said.
https://www.reuters.com/fact-check/...lethal-military-force-us-citizens-2024-10-31/
...}