Russian Pres. Vladimir Putin on Tuesday signed a decree revising the country's nuclear weapon doctrine, lowering the threshold for when first-use of such weapons can be deployed.
According to the publicly available document, scenarios in which a non-nuclear country attacks Russia with the involvement or backing of a nuclear state will now be considered a joint attack in which a nuclear response is possible. The same applies if a non-nuclear attack is deemed a critical threat to the nation's sovereignty, as well as that of its ally Belarus.
Putin is sending a clear signal to the West by concerningly upping the rhetoric around Russia's use of nuclear weapons. In making such a move, he is hoping that Western nations will think twice before continuing to support Ukraine.
These revisions to Russia's nuclear doctrine were put forward long ago and were approved as scheduled. This is unrelated to the US escalation of the conflict.