I suspect Russia has decided its time to settle things once and for all...its a excellent time. The US has signaled it will not launch on warning and so we are telegraphing we will ride out the opening attack and hope we still have forces left to respond. Unlike our weak Government who thinks a nuclear was isn’t winnable the Russians are not under that illusion.
The world knows more about nukes than it did in the Cold War. Land missiles are also only a third of the picture — 2/3 is something more than a “hope.” Russia knows MAD is still MAD.