The Kremlin has good reason to believe that NATO Article 5
will not work. It is just a piece of paper that actually means nothing,
just as it happened in the case of the Budapest Memorandum.
By attacking Ukraine, Russia violated the Budapest Memorandum
signed in 1994, according to which Ukraine gave up nuclear weapons
on its territory in exchange for guarantees of territorial inviolability
(
the signatory's independence and sovereignty in the existing borders).
The Memorandum was signed by Ukraine, Russia, the United States,
the United Kingdom. France and China and turned out to mean nothing.
This is a great shame for its signatories. The agreement to the Memorandum
was one of the biggest mistakes in the history of Ukraine, which in exchange
for a meaningless piece of paper signed by frivolous Western politicians
(Bill Clinton, John Major) got rid of the real force of nuclear deterrence.
https://en.wikipedia.org/wiki/Budapest_Memorandum
I am referring here rather to Western leaders (of NATO countries)
who haven't done enough to ensure that the Memorandum was not violated.
So can one trust them to uphold Art. 5?