You are wrong.
The posse comitatus act, within its very text, allows / authorizes the President to use regular military in the US when the civil authorities in an area fail to secure the Constitutional rights of their citizens.
President Trump paraphrased this in his speech tonight.
[I]n all cases of insurrection, or obstruction to the laws, either of the United States, or of any individual state or territory, where it is lawful for the President of the United States to call forth the militia for the purpose of suppressing such insurrection, or of causing the laws to be duly executed, it shall be lawful for him to employ, for the same purposes, such part of the land or naval force of the United States, as shall be judged necessary, having first observed all the pre-requisites of the law in that respect.
Insurrection Act of 1807, ch. 39, 2 Stat. 443, 443
and...
https://www.law.cornell.edu/uscode/text/10/252
10 U.S. Code § 252.Use of militia and armed forces to enforce Federal authority
Whenever the President considers that unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings, he may call into Federal service such of the militia of any State, and use such of the armed forces, as he considers necessary to enforce those laws or to suppress the rebellion.
(Aug. 10, 1956, ch. 1041, 70A Stat. 15, § 332; Pub. L. 109–163, div. A, title X, § 1057(a)(2), Jan. 6, 2006, 119 Stat. 3440; renumbered § 252, Pub. L. 114–328, div. A, title XII, § 1241(a)(2), Dec. 23, 2016, 130 Stat. 2497.)
You are wrong.
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Would not be the first time. And chances are it will not be the last time.