Russian President Vladimir Putin said Russia was changing its nuclear deterrence doctrine so that an attack by a non-nuclear state backed by a nuclear-armed ally would now be viewed as a "joint attack.

President Vladimir Putin warned the West on Wednesday that Russia could use nuclear weapons if it was struck with conventional missiles, and that Moscow would consider any assault on it supported by a nuclear power to be a joint attack.

The Times notes that Putin’s remarks signal that any “Western support for a conventional attack of Russia by Ukraine should be considered a joint attack and could, under certain circumstances, merit a nuclear response.” Given this context, the message from Putin to the U.S. with his public policy proposal seems to be pretty simple: Don’t try it.