However the world let the annexation of Crimea slide in 2014 and that emboldened Russia. Let them chop off a piece of Ukraine now and that will embolden them even more. After all Finland was a province of the Russian Empire before the revolution of 1917 and parts of Poland were under Soviet's control prior to 1941. And that's without going back into middle ages. Lots of places to take back.
In fact, it won't even really be the voting citizens of the USA who make any decisions, because when red/blue splits 50/50 it isn't "tyranny of the majority" anymore, it's tyranny of luck.
Re: your taxes - it'd be prudent to look beyond short-term effects and consider what different scenarios would lead to in the long-term. The EU had no choice but to help Ukraine to resist. Consider where things would've been now if they didn't.