True, except under specific conditions only in wartime. Trump will declare war on the invasion when he takes office. When the conditions of the Law of War manual 11.3 are satisfied, NG can be assisted by the Marines on American soil to remove the foreign invaders.
Only the US Congress can declare war. Trump can declare a national emergency and the incoming Congress will likely support him. (Unless Thune stops it.) I'm only pointing out the steps required.
EDIT:
Yes, I misspoke. National Emergency, not War. Results - Use of military on domestic soil.
It can be done, he just needs to do it the exact right way to forestall the lawsuits that the leftists will file.
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