US, being half a globe away from both conflicts has nothing to loose and everything to gain here.

Neither.

Ukraine falls: Putin gets marginally stronger, maybe even gets respect from CCP, Taiwan gets shafted.

Ukraine wins: Putin gets reckt, Russia gets chewed on by CCP instead of Taiwan. Slight chance of nuclear rain.

Israel falls: ugh... That means Iran got seriously underestimated. Also, no more US bases in ME. Isis fights Iran co instead. CCP proceeds to chew on Taiwan.

Israel wins. Things get messy for a while. Some domestic riots springing here's and there.