The US is peculiar with its nuclear policy in trying to guarantee immediate response
This doctrine is called "launch on warning". It hasn't been official US policy for 20 years[1]: In 1997, the Clinton administration changed the official policy away from launch on warning to one of retaliation after withstanding an initial first strike.
I'm referring to the policy of still maintaining the systems necessary to launch on warning, past promises about how the systems will be used are just PR.
It's not like in a hypothetical scenario where Russia has launched hundreds of ICBMs at the US in a first strike scenario Trump (or any other president) is going to feel beholden to some promise Clinton made in the 90s.
The president has absolute power over when and how to launch nuclear weapons, and can do so at a moment's notice, as has been covered extensively in the media in the last year where people seemed shocked that the president had this power since they didn't like the new person in office, even though the power itself hasn't changed in more than half a century.
This doctrine is called "launch on warning". It hasn't been official US policy for 20 years[1]: In 1997, the Clinton administration changed the official policy away from launch on warning to one of retaliation after withstanding an initial first strike.
[1] https://en.wikipedia.org/wiki/Launch_on_warning