"Soviet Stratgy for Nuclear War" by Douglass and Hoeber said that they deliberately planned on avoiding taking out POTUS as they felt it was important to have him alive to surrender. In addition to satisfying their need to a "legal" end to hostilities, they felt that way the Amercian people would be more inclined to accept the "inevitable".
Except of course how to develop an political and economic system that would take advantage of human nature and provide the most prosperity for the most citizens, thereby generating the tax dollars neccessary to defeat the US so they could implement their diabolical "let the POTUS live so we can conquer the US more easily" strategy.