America’s geopolitical role is changing. A person who has a keen understanding of this is journalist David Sanger. There was a time when the United States believed a post-Soviet Russia and a more economically friendly China could eventually be open to western Democratic norms. But, as Sanger discusses in his reporting, including his book “New Cold Wars: China’s Rise, Russia’s Invasion, and America’s Struggle to Defend the West,” that time seems long ago.