As I explained here
viewtopic.php?p=2532983#p2532983 it's important to recognize that NATO is an entity with its own interests.
The interests are
1) Maintaining its fig-leaf of "relevance" so that US and European govts continue to pump its babucracy with virtually unlimited funds
2) Not having to actually fight or risk any losses.
If Putin invades Ukraine it's a win-win for NATO.
Ukraine is not currently in NATO because its borders are disputed and it's embroiled in a current conflict (therefore, it cannot be inducted per the terms of the NATO charter).
If Putin does not invade Ukraine, and some sort of stable peace agreement is hammered out between Kiev, Moscow, and the Crimea/Donbass republics, there is a chance that the new Ukraine (with post-agreement borders) would become eligible for NATO membership in the coming months/years. However, if Putin invades, that eliminates the chances of Ukraine being inducted into NATO for the foreseeable future.
This serves NATO's interest number 2.
However, the whole drama of an invasion would allow NATO to present itself as the only shield between US-allied European countries and a newly aggressive Russia. This serves NATO's interest number 1.
The Americans frequently accuse Putin of wanting to perpetuate instability as his endgame. However, that is exactly the endgame of NATO in this situation: perpetual instability, at least in Ukraine.