This won’t happen, but if it DID happen, it would be interesting to see how the Feds would enforce it in (say) Texas. Or Oklahoma. Or North Dakota. Or Wyoming.
I'm sure it would be implemented as a period of time that citizens had to turn in their weapons, after which very high penalties would be imposed for possession.
They wouldn't assume 100% compliance, they would just be happy with the 75% compliance they did get and the knowledge that the other weapons would be collected (and owners punished) over time.
It would all be very low key.
I think the secession movement here in texas would go into high gear, warp speed actually. Probably much of the Red L states might follow, not sure. Also, probably would be followed shortly there after by a rapid demographic shift of populations. Some transplants and other assorted liberals would migrate to Blue states and vise versa. Sooo, would be a lot of uncertainty and a state of flux for the foreseeable future for sure. Probably a little shooting for awhile too. But, keep in mind that the military is very conservative. So this would be another shaking out too. Would be interesting times for Sure.
"Sternly worded letters" to our Governors and Fed agencies? Chest beating threats via the MSM? They'd be too chicken to send armed forces in to take what they cannot have.
Obama and his fellow travelers in Congress can say what they like, or decree what they like, but they don't have the power to disarm us. Only we do.