For the first time since the end of World War I, the president of the United States is not the leader of the free world. When the guns fell silent at the end of the Great War on Nov. 11, 1918, Europe was in ashes after more than four years of fighting. America was newly ascendant, a leader in manufacturing, science, military power and global influence – with a home front untouched by the destruction of war. Our leading role as the most powerful and influential nation on Earth was solidified with our victory in World War II. We never...