The way I see it is that the US is a federation of 50 nations. so if he wants to lock down his nation, he has the power to do that.
“so if he wants to lock down his nation, he has the power to do that.”
No, he doesn’t. He cannot declare himself dictator.
If he declares martial law. Otherwise the states can be requested to lock down and that is all. The federal government could also ban travel across state borders. Those two actions are about all the president could do.