US hegemony has been fading for years, unity in "The West" has faltered, and the world is moving back to a multi-polar framework. Post-war institutions are failing, though some or many may linger for years to come. The US must begin to reassess commitments around the world and determine if it makes more sense to cling so much to the Old World and legacy alliances, or shift focus to more overt hemispheric domination to procure stable physical resource availability and then selectively engage with current allies - and/or "enemies" as needed - to meet shifting economic and security needs. The US will continue to possess some advantages for years to come, not the least of which are two big oceans, so limited military engagement offshore balancing would serve as a useful possible grand strategy.
The fate of Ukraine and other individual nation-states may not have a material or even any impact on US security or economic interests. Taiwan is of course different given the questionable series of decisions that led it to become so crucial a source of critical contemporary resources (eg, semiconductors), but judicious mercantilist policy choices - subsidies, tariffs, and non-tariff trade barriers - can help bolster critical industries domestically. Nothing happening now necessitates direct American military action, and if Russia does invade Ukraine - and Biden said the decision has already been made to do so - then the decline of relative American power and the weakening of post-war institutions will accelerate slightly, or maybe more than slightly. Perhaps, if Russia does invade Ukraine and faces only sanctions, retaliatory cyber warfare, and sternly worded memoranda in response (though it seems tactical destabilization policies in the Caucasus and Central Asia could also be pursued), then maybe he eyes the Baltic nations to put NATO to a real test. That seems like a very European problem.
