"NATO is committed to the principle that an attack against one or several of its members is considered as an attack against all. This is the principle of
collective defence, which is enshrined in Article 5 of the Washington Treaty."
No matter what, an attack on a member will hurt, and that in it self makes an a potential attacker think twice.
Lets be real, if the Baltic was not in NATO, Russia would probably done a Crimea a long time ago.
At least now they will think once or twice before attacking.. And yes NATO will counter.