Pick an international boogeyman, any international boogeyman, sometime in the not-too-distant future. It could be Red Chinese Hordes, done eating up East Asia and hungry for more. It could be the Apocalyptic Army of the Caliphate, storming our gates to install sharia over America. A resurgent, revanchist Russia. Nazis. Heavily-armed Jehovah's Witnesses.
Whomever you chose, imagine that they've invaded our great nation. We're at war