Before making chest-thumping proclamations of this sort perhaps you'd best read the text of article 5:
-- If a member is attacked, other members will take "such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area".
See the part where it says "such action it deems necessary"? Trump may decide that the necessary action is to go play golf. He's gone back and forth on his commitment to European defense a number of times over the years, so there's really no reason to believe that his he won't change his mind on it before breakfast tomorrow.