An attack on former Ukraine regions now part of Russia will be considered an attack on Russia. How will Putin respond to an attack?

FIRST: they’re NOT “former Ukraine regions” - they are the sovereign territory of Ukraine, internationally recognised as such, and no bullshit, trumped up “referendum” knocked up In days, in the midst of war and for regions of Ukraine that Russia doesn’t even fully possess, will change that fact.

Next: will Putin use nuclear weapons - his, what, sixth, seventh threat to do so since February - if what he CLAIMS is now “Russian territory” continue to be attacked by Ukraine’s liberating forces backed up by Western and NATO supplies, intelligence, training and hardware? One answer to that:
Why?
1. Russia knows that it’s claim that the annexed territories won’t be recognized under international law.

2. China will NOT support the disastrous use of such weapons and, if Russia does it, China will cut it dead and leave it flying solo (apart from the mighty military juggernauts of North Korea, Iran and Duria, of course…!)

3. Economic sanctions will become both fully comprehensive and virtually universal as virtually every country reacts to this massive line crosser.

4. NATO will 1 I repeat will - respond. There will be a massive build up of conventional land, sea and air forces, almost every plane and ship that tries to move beyond Russian waters and airspace will be intercepted, tuned back or impounded, above all, the flow of supplies into Ukraibexwill be an absolute torrent.

5. even the modest act of limited mobilisation has ripped open the fragile and sullen compliance of the Russian people. This will unleash a shit storm inside the country.

Even just one or two of these points is ‘endgame’ crippling to Russia and it will never - NEVER - dare to go toe to toe with NATO, not by either initiating a nuclear exchange with it (NATO simply will not first strike) let alone take his fifth rate armed forces against the overwhelming might of the planets greatest, largest and most technologically advanced military alliance.

So, Vladimir, in the words of ‘Pulp Fiction’: