Vladimir Putin draws a nuclear red line for the West. How credible is it?

economictimes.indiatimes.com:

Putin has now backed the threats with a revision of the country's nuclear doctrine. He has announced plans to broaden Russia's rules on the use of its nuclear weaponry, just when the West is considering allowing Ukraine to strike deep within Russia with long-range Western missiles.

Putin had recently warned that long-range missile strikes into Russia by Ukraine would mean Nato is at war with it.

Kremlin spokesman Dmitry Peskov said the planned changes «must be considered a specific signal». «A signal that warns these countries of the consequences if they participate in an attack on our country by various means, not necessarily nuclear,» Peskov told reporters.

Without mentioning Ukraine by name, he said Russia's "nuclear deterrence is being adjusted on account of elements of tension that are developing along the perimeter of our borders".

What are the proposed changes in Russia's nuclear doctrine?
A proposal by Russian President Vladimir Putin to update the national nuclear doctrine was brought up at the session of the Russian Security Council on Wednesday, RT reported. The first proposed update to the nuclear policy “expands the category of states and military alliances” to which nuclear deterrence applies, and “supplements the list of military threats” intended to be neutralized by the deterrent.

This would treat “aggression against Russia by any non-nuclear state, but with the participation or support of a nuclear state” as their “joint attack,” crossing the nuclear threshold. The change means Russia can attack Ukraine even though it is a non-nuclear state if it mounts an attack on Russia with help of the US or NATO.