Nobody in, or out of there mind is going to premptively strike at a carrier group, unless they think that all out war is inevitable.
They immediatly loose the
PR war by going first, and the obvious response is too great. I would think they would have a go if, one they where totally sure they where going to be getting a good smiting.
Or after some surgical strikes or other significant action by the US, in which case I would have thought the carrier group would not be in a vulnerable position due to the obvious risk.
Mind you there's always the chance of a good old fashioned balls up.