Red states would tell him to piss off.
Then it’s civil war.
Only that, under Obama I took a deep breath and did some research on the President’s power to outlaw gun ownership with the stroke of a pen. It just isn’t there, because it omits the role of Congress and they are very protective of their turf.
Remember that we already have had Democrat control of Congress under JFK, LBJ, Carter, Clinton, then Obama. Damage was done to the 2nd amendment but was later much undone by Reagan & later Republicans.
The SCOTUS will soon have a conservative majority, barring assassinations, and this will be a major thorn to a Democrat majority if God forbid that comes to pass.
Of course the Democrats now have a new weapon: surrounding their opponents’ homes with Antifa/BLM. But recall that the same happened to Justice Clarence Thomas in 1991: Al Sharpton & his homies surrounded his house but the police ordered them to back off; Sharpton threatened a sit-down hunger strike but chose to leave; no port-a-johns nearby.
Confiscation requires manpower and that takes more than just declaring all LEO’s to be Federal agents. It may take no more than a handful of pro-2A governors to declare that they will not cooperate in any way with Federal confiscation or Red Flag and at that point Harris-Biden will have to decide whether to turn their antigun initiative into a shooting war.
Or even worse, they will import millions of Californians & illegals into red states. Or is that happening now?