How will they know unless gun registration is part of their little scheme?
Ahh, but that's the trick isn't it? and the next shoe to drop... You see, the backers of the so-called "universal" background checks KNOW they are completely and utterly unenforceable as Colorado has found out without one successful prosecution to date and only an estimated 13% of private gun sales bothering to jump through the background check hoop. Since there is no record of who owns what guns and many if not most have already changed hands multiple times over the years, the government doesn't have the slightest idea how many guns are owned or who owns them any more than they know how many ball-point pens are owned and by whom. Hence, any "universal" background check systems is essentially on the honor system. If I sell a gun to my buddy Joe and don't bother to get the background check done, how does the government know I violated the law? Unless I'm stupid enough to write Joe a correctly dated receipt or Joe is stupid enough to pay me with a check (with Magnum .44 Serial Number 12343412 in the memo line) they don't.
So the next show to drop will be, "Those rascally gun owners are ignoring our precious universal background check system and we have no way to monitor or enforce it! But we have a simple "reasonable" fix! A law requiring all guns in the state to be registered, so we can monitor and enforce it, but for no other reason like future confiscation. Trust us.. (wink,wink)."