It is difficult to explain to your average American why they should care about a place like Ukraine.
Unlike most of Europe, Ukraine has scant relevance to American interests. Gas transiting through Ukraine has zero impact on American fuel supplies. Beyond that, despite being independent for more than 30 years, the country hasn’t developed into a functioning democracy. You can lead a horse to water but you can’t make it drink, an old American saying goes.
In fact, pretty much the only worthwhile argument is based on principle.
In other words, Ukraine wants to be a thriving, independent democracy and those are values that Americans should support. When such values are threatened by a bully, moral people everywhere should be appalled. As of today, that is still the position held by most top American politicians — Democrats and Republicans. But much more than principles, politicians care about reelection, so there is no guarantee it stays that way.