Does it matter if not all tactical weapons are delivered? The point is escalation. There is no meaningful defense against ICBM/MIRVs. Also, you can rest assured

Does it matter if not all tactical weapons are delivered? The point is escalation. There is no meaningful defense against ICBM/MIRVs. Also, you can rest assured that a regime that launched nukes first will not be susceptible to decapitation.