1) A lot of discussion centering on why Trump "doesen't send in the troops." Sounds reasonable, but likely isn't Constitutional.

2) It probably (yet) isn't a good idea politically either.

3) In 1878, as a response to federal (Union) troops in the South enforcing . . .

3) contd . . . civil rights laws, Congress passed the Posse Comitatus Act. This, in concert with the Insurrection Act of 1807, was to limit the powers of the federal government in using federal military personnel to enforce domestic policies within the United States

4) In short, Congress did not want a President taking over cities militarily using the pretense of an insurrection to do so. The Act was part of an army appropriations bill.

5) Interestingly, it specifically ONLY refers to the US Army and the US Air Force (amended in 1956)

6) By actual wording, neither the USMC, Coast Guard, nor Navy are prohibited from actions contained in the Act. However, the "spirit of the law" would certainly be held that they likewise are constrained.

7) "it shall not be lawful to employ any part of the Army of the United States, as a posse comitatus, or otherwise, for the purpose of executing the laws, except in such cases and under such circumstances as such employment of said force may be expressly authorized . . ."

7) contd . . . "by the Constitution or by act of Congress." It goes on to say money cannot be appropriated or spent for such purposes AND "any person willfully violating the provisions of this section shall be deemed guilty of a misdemeanor and on conviction thereof . . .