Middletown, Va.

Troy Carter, 49, says that, other than voting, he’d never been involved in politics. That changed late last year, when he heard that a county board of supervisors in Virginia voted to become a gun sanctuary. On Monday he was one of an estimated 22,000 people who gathered peacefully at the Capitol Square in Richmond, Va., to support gun rights. Many of those attending were visibly armed.

Ninety-one...