The National Guard is only authorized in the first place by the US constitution, and every member of the National Guard swears an oath to support and uphold the US constitution against all enemies (foreign and domestic), and also to obey the president of the US.
The idea that the national guard will rise up against their own commander in chief is a fantasy. We've already seen how it plays out when states raise an army against the federal government and it doesn't work out very well for them.
Even if (and it's a big if) the military didn't agree with Trump specifically, they'll still largely believe in the country and the constitution. If the federal government does something terrible and unconstitutional enough that it becomes necessary for states to attack the federal government they will have abandoned anything resembling 'state's rights' and moved into lawless/oath-breaking civil war.