He wasn’t able to do it in 2016 for the same reason this time around— probably, anyway. My guess is it’s mostly not a priority compared to enriching billionaires, but also some Republicans probably aren’t that interested in overthrowing State governments (especially Californian house members lol). You also have the issue of compliance, as the military and FBI aren’t exactly Hitler’s generals. Yet, anyway.
I mean, it’s the whole point of the “states rights” things. Republicans use that hypocritically, but there’s truth to it. But you’re right in that it’s been eroded for a long time; that and the executive branch has gained more and more power too. Constitutionalists should be up in arms but again, hypocrites every last one of them.