JACKSON, Ga. — “Put the guns down!” The order crackled over a loudspeaker from two sheriff’s deputies crouched behind the doors of police cruisers, semiautomatic rifles at their sides. Several middle-aged militiamen were toting loaded AR-15 rifles and 9-millimeter pistols at a makeshift checkpoint — two lawn chairs and a narrow board — on a dirt driveway in central Georgia. The men, members of the Georgia Security Force III% militia, grumbled but laid their weapons down on the red clay earth. The brief standoff ended with an amicable chat, and the men retrieved their weapons the moment the lawmen drove...