NATO enlargement has been the policy of the United States since Bill Clinton was elected president in 1992. The course of action he adopted was embraced and extended by successors George W. Bush and Barack Obama. Was it a good idea? Anne Applebaum thinks so. The Pulitzer Prize-winning author and journalist has been among NATO expansion’s most ardent advocates since becoming a correspondent for The Economist in 1988 and moving to Warsaw. In a panel podcast last week for The Atlantic, where she is now a contributing writer, she said, I think that the expansion of NATO was the most…