that's what everyone thought would happen with Ukraine, and Baltic statse will have full support of nato
NATO is doing everything it can to avoid war now but i'm pretty sure everyone is preparing to react in case member is attacked
"The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all"
Every country has an obligation to defend itself when attacked. Article 5 makes an attack on any member an attack on all of them.
Short of going "fuck y'all this agreement means nothing to us" every member country has to defend against the attack as if it were on their own soil.