If they do, all bets are off, and the citizens of the US will arm themselves to the teeth. The US Constitution is the law of the land, not UN treatises or decrees.
If congress wants to challenge that fact, they’ll face a literal shitstorm of blowback.
We already are, they (Obama et al) know we are, and that knowledge is all that's holding them back.
I have one even better for you...
My right to own weapons doesn't rely on the Constitution, that right is unalienable (a natural right) and the Constitution merely states that our government is supposed to protect that right.
THAT is what gun control control freaks don't want everyone to know.
(Oh, wait...people don't understand natural rights as they don't even know what a natural born citizen is under natural law. Never mind.) /sarcasm