A day after Putin belligerently welcomed four Ukrainian provinces to the bosom of Mother Russia a key city, Lyman, in one of the provinces, Donetsk, has been abandoned by Russian troops. Putin has stated, and it is long Russian (and prior, Soviet) doctrine that newly-conquered territory is to be defended with all weapons, including nuclear, as would Moscow itself.
And on that note a close Putin ally, Ramzan Kadyrov, the leader of the southern Chechnya, writes today,
"In my personal opinion, more drastic measures should be taken, right up to the declaration of martial law in the border areas and the use of low-yield nuclear weapons."
Finally, earlier this week Ukraine applied for expedited membership in NATO, Article 5 of whose charter calls for collective defense (individual countries can opt out) of an attacked member.