Is European defense becoming a necessity?

With a resurgent Russia on one side, and a US that is sending mixed signals about its commitment to NATO and European defense, does Europe need a back-up plan? Max Bergmann, the director of the Europe, Russia, and Eurasia Program and the Stuart Center in Euro-Atlantic and Northern European Studies at CSIS, joins Thanos Davelis too break down why European defense is likely becoming a necessity.