Andrew J. Bacevich thinks our political system is busted. In “The Limits of Power: The End of American Exceptionalism,” he argues that the country’s founding principle — freedom — has become confused with appetite, turning America’s traditional quest for liberty into an obsession with consumption, the never-ending search for more. To accommodate this hunger, pandering politicians have created an informal empire of supply, maintaining it through constant brush-fire wars. Yet the foreign-policy apparatus meant to manage that empire has grown hideously bloated and has led the nation into one disaster after another. The latest is Iraq: in Bacevich’s mind, the crystallization of all that’s gone wrong with the American system.