As far as first use of nukes is concerned
The US has the same policy as Pakistan: And we used to have the same reason for it that Pakistan does.
When your territory is liable to be invaded by a superior force, then to deter that force, it's a good idea to put out the idea that you will or may retaliate with nukes. With the fall of the Sovs we lost the basis for this strategy.
I guess a case could be made that at some time in the future, we may be threatened with a superior land force again.