. . . What I mean is that Gun Control politically and legally was at its apex of power and influence in the 1990s. In that period the courts and legal schools were dominated by the "collective right" interpretation of the 2nd Amendment, the idea that the 2nd was an Individual Right was practically laughed out of the academy (no, seriously, I have Intro Constitutional Law textbooks written the year before DC vs Heller and it barely gives a few paragraphs to the Individual Right interpretation...), and the Democrats succeeded in passing a Federal Assault Weapon Ban and the Gun Control advocates in Congress were starting to even go mask off about wanting to ban all firearms banned and outright admitted to salami slicing tactics...
And even back then they knew that a blanket semi-automatic ban wouldn't have managed to be upheld in the courts. They never even tried it because they knew it was a bridge to far. To try this now, after Heller and Bruen have completely changed the calculus on 2nd Amendment jurisprudence seems utterly insane as even more gun control favoring Courts are going to treat this kind of ban with exceptionally heightened suspicion and likely be hostile to it.
. . . That you think this is laughable. Splitting the US in two would create two countries that are occupy the number 1 and 2 slots of world economic and military power over Russia and China. Given the likely makeup of the "Based" US (being mainly Appalachia, the Midwest and South plus potentially Alaska) that is a lot of agricultural, resource, and technology base to "isolate" from the world (and they wouldn't want to, they'd want to trade with it), with a large population and enough resources they could be self sufficient, as well as plenty of ports to build a navy out of. The other successor states would also have considerable economic power to leverage.