Sanctions? As you may know we don't have an army. What else do you suggest?

If western europe was looking to square up to Russia to protect an eastern europe buffer zone, they could have used the Budapest memorandum on security assurances as a pretext to offer military assistance the moment Russian troops started crossing the border.

One could reasonably argue that Ukraine simply wasn't part of the EU, and if Russia threatened Poland it would be a different matter. That it is the EU membership, not the buffer zone, that is important.

Another possible interpretation is EU would have wanted to intervene, but its current political structure proved too deliberative to react before it was too late. That would imply an EU army would also need political reform.

Crimea is/was part of Ukraine though not part of EU. There are still active sanctions over Russian activities there and were recently renewed.

No idea, but the point I was responding that Europeans would never let Russia dominate a border country, and the Ukraine seems like a counter point.

Ukraine is Russia’s buffer to NATO, not the EU’s buffer to Russia.

Crimea already had a major Russian naval base in it.

By that logic, there would be nothing to complain about if the US takes over the German state of Rhineland-Palatinate since they already have an air base there (Ramstein).

No, by that logic Russia or someone else would hesitate to attack Germany because of the US airbase. Just like the EU and the US hesitated to defend Crimea because of Sevastopol.