Over the past few weeks, a growing sense of alarm across Europe over the future of the continent’s security has turned into outright panic. As Russia advances on the battlefield in Ukraine, the U.S. Congress has refused to pass billions of dollars in new funding for Ukraine’s war effort and Donald Trump has warned European leaders that if they do not pay what he considers their fair share toward NATO, he would not protect them from Russian aggression. Steven Erlanger, the chief diplomatic correspondent for The Times, discusses Europe’s plans to defend itself against Russia without the help of the United States.