What is the theme in Clear and Present Danger by Tom Clancy?

Threats to national security is a theme in the book. The title of the book, "Clear and present Danger" invokes the concept of threats to the security of the United States. This condition allows the President to order judicious use of military force to protect the safety of the citizens of the United States. The definition of what exactly is a threat to national security is the main underlying theme of the book.