I don't think the US ever "rushed in" to attack Russian forces; even in the heated 1960s, people thought long and hard before pushing those nuclear buttons. There are many ways to provide military aid, not all of them involving your own troops; and with the rise of a strongly anti-Russian EU Commission, I bet all these options will be considered sooner rather than later. At the end of the day, it took years for NATO to intervene in Yugoslavia, a situation far less problematic than Ukraine (from the point of view of Russian engagement); but then they did intervene, twice.
In the grand scheme of things, EU defense relies immensely on US forces and there are no signs that this is going to change anytime soon. The UK is struggling to just maintain capability, let alone expand it to replace allied resources. The French are now 100% integrated in NATO and have enough on their plate by caring for their African ex-colonies anyway. Italy and Spain can't pay state pensions, let alone expanding their military. The only country with some spare capacity would be Germany, which cannot do it for historical and political reasons.
In fact, what the Ukraine crisis is showing is how Europe still cannot say no to the US in security matters: it was the US administration that pushed for escalating Maidan (remember "fuck the EU"?), it was the US administration that pushed for sanctions (with Europeans going along grudgingly) and it's the closest US allies (UK, Poland) who are now leading the charge for further escalation... and finding no formal opposition, despite plenty of grumbling across the continent. Because in practice, nobody can afford to lose their US umbrella.
As a U.S. citizen, I have been extremely confused about why there has been no global response to Ukraine, especially from Europe. You seem to be implying that the EU does not care about Ukraine at all and is only responding to the crisis there to the extent the US is pushing for it (i.e., not very much).
Why not? Surely Europe doesn't want to set a precedent that Russia can foment and fund an "opposition", claim the existence of such an opposition means that the territory it is in should be annexed, and then annex it. I would have expected that Germany of all countries would recognize these tactics for exactly what they are: almost a direct replay of Hitler's pre-WWII tactics. It should be all the more galling because the proximal cause was that Ukraine was too "pro-EU". Yet the EU doesn't lift a finger. AFAICT, Obama doesn't do much because he is more concerned about ISIS, and sees Ukraine as a European problem.
That may change more swiftly than you imagine. It seems like the US is already far more reluctant than ten years ago to go rushing in.