Why should they have a "unified front" in an irrelevant peripheral war?
>They failed to provide any military deterrence to the Russian federation
Because the "Russian federation" is a viable antagonist for EU?
If anything, the US overestimates how important its "shield" is, as if they are some kind of cavalry and EU a damsel in distress.
US involvement and NATO are mostly remnants of the Cold War, when USSR and its satellites in Eastern Europe was indeed a formidable antagonist for the European countries. The US, due to its size and economic/diplomatic influence still has lots of European politicians by the balls, and can buy others. This is what prevents an EU-driven NATO-like body.
That, plus the fact that EU is just a loose union of different national countries, and not an actual federation of a single people, like the US is, and European national interest don't always see eye to eye.
Russia is of little consequence in the European state of affairs/influence, and fundamentalism terrorism from the failed states is a mess the US created and/or fueled, and which European powers like France and UK could have handled 10 times better (and had, in the past).