Literally everyone else in NATO is closer to Russia's sphere of influence and therefore in more danger than we are, yet none of them are making commitments to send troops to Ukraine, and most aren't making commitments to send weapons and other gear. As far as I know, not all are even onboard with the idea of sanctions. If they're not alarmed at "staring down the jaws of the Russian Bear," why should we be alarmed on their behalf?

As far as I'm aware, there's no treaty or agreement between the US and Ukraine, at least not in the terms you're describing. If Russia does indeed invade Ukraine, we're not compelled to act by anything other than our own geopolitical interest, since Ukraine is not a member of NATO.

Is that to say we should sit on our hands and do nothing? No, of course not. But neither is it to say we should declare war on Russia in that event. The cold truth is that if we were to do that, there's a very good chance of things spinning out of control and ending up as more than a regional conflict. I see where you're coming from regarding standing up to Russia, but that's not a line the US wants to cross without allies at its back, and right now, those allies just aren't here for it.

The only way they would be is if Russia were to attack a NATO state, and I don't think Putin is that stupid.