I have to question what backing the USAF could give. Vietnam is never going to let the USAF operate from there, the Philippine's wouldn't want to royally **** off China by playing host, so that leaves South Korea and Japan as the only friendly airbases they could stage from.
That's a 1600+ mile round trip. The F-16 cannot do it, the F-35 would be returning on fumes, the F-15 might be able to but would need to enter the combat zone and fight with it's external tanks still attached as they would be required to make it back to base (this would also limit the weaponry it could carry), the F-22 would be in a similar situation but the tanks would 86 it's stealth capabilities. It would be a very bad engagement for the USAF any way you slice it.
Obviously much could be mitigated by using aerial refuelling tankers to resupply them before the enter the combat area and on their way back. But the issue with that is if China are invading Taiwan and fighting the US Navy they aren't going to care about shooting down some aerial tankers in international airspace and if they did that with USAF jets in the air they may not make it home.
So I doubt the USAF would really be tied up much with China if they went full idiot too, as there's not much they would really be needed for, and so could focus fully on Russia.