There's nothing the US can do any more to stop Iran developing a nuclear weapon. They have just proved that peace talks don't work, negotiations don't work. The only way to defend yourself from America is to have the actual capability to nuke Washington DC from afar. And Iran has a right to defend itself, so it will develop that capability.

What would be the consequences? The same thing that already just happened? America punished them, killed their head of state as revenge for not having a nuke yet.

The US could do pretty much whatever it wants with Iran tbh. Iran’s entire navy is sunk. They have no functional air force. There’s also the obvious way to straight up finish them off, but the cost to Iran’s civilian population would be enormous and it would be unprecedented.