Why? China is probably prepared to invade Taiwan. A russian invasion would give china cover for their own actions. What would Biden do?
I'd bet Biden would not congratulate and compliment them on being strong. Nor would he toss the citizens of Ukraine or Taiwan paper towels in a photo op.
If Russia invades Ukraine and China invades Taiwan simultaneously how would the US react? What would Biden do? Whatever he's told. ... and then he'd ramp up the Jan 6 thingy. We got the wrong Biden at the helm. We need the other one.
America fought an Atlantic & Pacific front at the same time before w/o much starting foothold on either; ask how that went for the other sides.
How'd it go for Viet Nam? How'd it go for Afghanistan? Here's your rifle. Here's your parachute. Bye!
You are talking about a war that took place eighty years ago. There is no between then and now. comparison .