they would need a shitload of nukes, nukes are powerful but it takes a lot more than like 1 or 2 to destroy a country as big as america, especially with so much of our military spread around the world (our f35s and probably our older jets can carry nuclear weapons without necessarily being as obvious as an ICBM). even if they used hypersonic missiles to deliver a shitload of nukes they had been somehow building in secret for decades, it is likely we would be able to fire at least some of our own much larger arsenal of slower ICBM nukes before our launch facilities etc. are completely annihilated, and as we have seen in israel and ukraine, intercepting even conventional missiles is a lot harder than it might seem. that's not even getting into impacts on global weather/agriculture and loss of major economic trading partners, even before all that you have to account for the basic concepts of 'mutually assured destruction', we will nuke them back if they nuked us in a way that didn't completely destroy our nuclear capabilities. China might be able to make one or two surprise nuclear attacks with hypersonics but i doubt they could stealthily hit all of our launch facilities, nuclear submarines, and aircraft carriers and airbases with one wave of attacks.

we basically need like aliens with miraculous stealth technology to simultaneously infiltrate all american (maybe all world) nuclear facilities and equipment to deactivate/destroy it like a giant metal gear mission.