US action following a Taiwan invasion could be shoot a few missiles at the invasion fleet.

Declare all coastal areas around China a conflict zone.

Declare anyone trading with China can't trade with the US. If backed by allies, China could perhaps be boxed in.

But, hey, who knows. It's entirely unclear what is possible.

And much depends on whether Taiwan falls in 3 days, or stays in the fight for 3 years.

Or so one would assume.. current administration is proving that they'll abandon freedom at minimal cost.