Situation in Ukraine

[Starter]

Ukraine is not a member but we are. NATO constitutes a system of collective defence whereby its member states agree to mutual defense in response to an attack by any external party.

I'm aware of what NATO is and what its supposed to do. However, what it says it will do and what the current reality could be (and probably is) are two different things.

Not to mention, what about an internal attack ala Crimea and now Ukraine.