@randahl The reason is that Russia has a policy, predating Putin and regularly reauthorized, that if Russia is faced with defeat then they will escalate to first use of nuclear weapons. The definition of “defeat” gives them some wiggle room, but the threat is real. The military-political consensus seems to be that once tactical nukes are used then escalation to a broader nuclear exchange is inevitable. No country wants to get near that tripwire. Direct confrontation is avoided.