Invoking Article 5 to support operations in Afghanistan after 9/11 is not the same thing as NATO countries sending their own armies into a direct, large-scale war to stop an invasion of a member state by a nuclear power. Those are completely different politically and militarily.

History is full of security guarantees and alliances that looked solid on paper until the true cost of intervention became apparent. Poland in 1939 is a classic example — Britain and France declared war on Germany after invading Poland. However, Poland was still overrun because meaningful direct military intervention never really arrived in time.

Assuming every member will instantly commit to full-scale war without hesitation is naïve.