Kremlin spokesperson Dmitry Peskov said Tuesday that Russia's new nuclear weapons doctrine means Ukraine's use of Western rockets "can prompt a nuclear response."

After U.S. President Joe Biden gave the go-ahead for Ukraine to wield long-range American missiles deep inside Russia, as a Newsweek map illustrates, questions remain over just how much of a difference this will make as Moscow gains in the east and a new U.S. presidential term approaches.