The last nuclear arms treaty between the U.S. and Russia expired in February. And both Russia and China are testing weapons systems designed to evade US nuclear defense. CNN’s Krishna Andavolu explains how a new nuclear arms race is developing. 0:00 The new threat of 'fractional orbital bombardment' 2:35 Russia's nuclear-powered doomsday devices 3:57 What happened to our nuclear weapon treaties? 5:41 China's tactical nuclear weapons Watch more news explainers on the CNN app: https://cnn.it/