Trump might be bluffing, but Twitter can't possibly know.
https://kstp.com/news/minnesota-national-guard-activated-to-...
https://www.npr.org/2018/04/05/599895184/why-president-trump...
But he doesn't.
Also it is illegal for the federal government to use the military as a police force: https://en.wikipedia.org/wiki/Posse_Comitatus_Act