I would have thought that a US preemptive strike was already factored in.
There is no way the US is going to sit and wait for Rusk strikes before saying OK now we end this.
As soon as the US feels threatened, (or the UK for that matter) they are going to strike hard and fast in multiple locations to show that they are not pxssing about and that this stupid adventure has now come to an end.
The US could probably send a catastrophic message to Rusk sailors while still having culpable deniability...the message would still get through loud and clear.