That’s all correct, but I imagine that the wonder boy would simply sign an EO declaring guns illegal.
He could, but he would just be made to look like an idiot because the next day a dozen federal lawsuits asking for an immediate injunction of the EO would be filed and all it would take is one federal judge finding their is a reasonable chance the EO is unconstitutional (not exactly a high bar) and the EO would be stayed until it worked it's way through the court (and Obama would be out of office by the time that happened).
Hey, would we all have to take our guns to Washington,DC to turn them in? I imagine we would have to take the ammo with us, too? Sounds like fun.