THE .50 CALIBER Bushmaster bolt action rifle is a serious weapon. The model that Pvt. 1st Class Lee Pray is saving up for has a 2,500-yard range and comes with a Mark IV scope and an easy-load magazine. When the 25-year-old drove me to a mall in Watertown, New York, near the Fort Drum Army base, he brought me to see it in its glass case—he visits it periodically, like a kid coveting something at the toy store. It'll take plenty of military paychecks to cover the $5,600 price tag, but he considers the Bushmaster essential in his preparations to take on the US government when it declares martial law.

There are scores of patriot groups, but what makes Oath Keepers unique is that its core membership consists of men and women in uniform, including soldiers, police, and veterans. At regular ceremonies in every state, members reaffirm their official oaths of service, pledging to protect the Constitution—but then they go a step further, vowing to disobey "unconstitutional" orders from what they view as an increasingly tyrannical government.