Serious yes, but nuclear, surely not? If the US would use nuclear retaliation after a conventional attack (or more likely, a conventional defense, because nobody sane would attack a US carrier unless it posed an immediate threat) I think that would violate all doctrine on the use of nuclear weapons.

The entire official nuclear policy of every single nuclear power (as far as I'm aware) is that they will only use nuclear weapons in response to a nuclear attack or an existential threat. Officially. I believe Putin stated at some point that he would not consider the use of small tactical nukes to be nuclear escalation (if Russia does it), but I would expect the US to be better than that.

I can't imagine a scenario where our carrier fleet is in imminent danger that doesn't qualify as an existential threat. We haven't faced that since WW2 and Japan did end up on the receiving end of nuclear arms.

US carriers carry over 5,000 sailors, having one taken out would be almost unimaginable (a one time event with more US deaths than the Iraq and Afghanistan wars combined).

You might want to step back and just reconsider how riddiculous it sounds. 5000 soldiers over millions of civilians? Really? Existential threat would be invasion force / bombing run / missile strike coming to continental US territories. Anything else is just "they took our toys"

I don't think you know what "existential threat" means. It means your home country itself is in danger. Losing a single carrier only slightly reduces the US's ability to project force around the globe. But even with all carriers gone (not something that's ever going to happen), it would still be folly to attack the US on its own soil.

> The entire official nuclear policy of every single nuclear power (as far as I'm aware) is that they will only use nuclear weapons in response to a nuclear attack or an existential threat. Officially.

The US has never had such an official doctrine, nor to my knowledge has any of the other major nuclear powers.

>Initiating a nuclear war after a nation state starts taking out your aircraft carriers is not entirely unexpected.

Really? Should the US expect it too when it regularly does the same to third countries?

Of course the US does which is why it has such a serious policy of preventing nuclear proliferation. Part of these aircraft carrier's jobs is to protect allies so they don't feel the need to acquire nuclear weapons.

When was the last time the US took out another country's aircraft carrier?

1945, for others who don't don't know or care to check.

Quite the pedantic distinction. Bombing them is enough, except if magically taking out an aircraft carrier is worse behavior than bombing a city or invading a country.