Posse Comitatus is supposed to protect the American citizenry and it does a very good job of that. The National Guard has authority roles under Title 32 to support law enforcment activity with intelligence, logistic support, and even direct support for criminal busts if necessary. This is one of those “The DOD can’t do domestic!” but the list of approved domestic activities is a mile long.
That being said, the Oregon Governor lacks the authority to call up the national guard to go all jackbooted thug on a bunch of rednecks with rifles occupying a federal building in the middle of nowhere Oregon.
The President can. The legal requirement is a declaration of insurrection or rebellion, and then he can call upon the militia to put down the rebellion and enforce the law of the land.
And it is all completely legal under US Code 10 Section 331 through 335.
And if someone really did understand, support and defend the Constitution, they would know this. The Constitution generally lets a Federal Government do all sorts of things that violate the individual rights of citizens. Even “due process” has come to mean, “whatever process the Government decides is adequate” such as a “no fly list/terror watch list” or killing US citizens in foreign countries as collateral damage in the “war on terror.”
The Constitution is supposed to be a limiting document. But the limitation has largely become a paper drill.