18 U.S.C. § 1385. Use of Army and Air Force as posse comitatus
Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both.
Guards do not enforce law. a fine line I admit but still a line.
That is alot 'better' than a few years ago. When the Pres took over the National Guard[pdf]. Lol.