It’s the nightmare scenario, a major city destroyed with no warning. What if it is Moscow, instead of NYC? Or what if it is both at the same time?
Serious stuff, and the major players (US/Russia/Who else) do need to discuss this at some high level in terms in initial response and communication.
The smartest move the President would make would be ... do as thou wilt in the Middle East ... but spare Israel. we'll both pick up the pieces later.