Democrat progressives would likely unfavourably weigh Taiwan freedom against their domestic agenda. There’s no guarantee Republicans would reach across the aisle. Or look at the Biden Afghanistan press conference, that it is likely read as being tired of conflict and insufficiently committed to a protracted fight especially against a more evenly matched foe. Most NATO members couldn’t finish what they started in Libya. Finally Japan is reliant on US integration, the Chinese might be able to finesse the odds better (like the Russia deal) before striking and fancy their chances.