Tit-for-tat moves this week included the use of American-made ballistic missiles to strike inside Russia, and new nuclear threats from Moscow. Neither appear to have influenced the war on the ground.

Two days ago, Russian President Vladimir Putin announced a change in the country's policy for employing nuclear weapons in conflict. Then, on Thursday, Russia attacked the Ukrainian city of Dnipro with a new type of ballistic missile capable of one day delivering multiple nuclear warheads to distant targets with little warning.