I am aware that it is an American tradition to worry about Presidents defying their term limits, declaring national emergencies to seize power, and all that jazz. It's a tradition I approve of, especially given the increasing power of the executive branch, and Congress's weak-kneed approach to reigning that in.
That said, Trump's "jokes" about such things are not ordinary and are deeply inappropriate. Also his attempts to get the military and the police to show personal loyalty to him is also unusual, and deeply inappropriate. Even if, as you say, he couldn't pull it off even if he tried, that doesn't mean it is not setting bad precedent. Norms are much harder to build up than to tear down, and the rule of law as we know it cannot survive without them.