Here’s a legal poser for the New Year. The board of supervisors in Virginia’s Fauquier County has voted unanimously that it is a “constitutional county.” This is part of a larger movement by Virginia counties to declare themselves “Second Amendment sanctuaries” in anticipation of gun-control measures the new Democratic state Legislature is expected to pass in 2020.

Eighty-six of Virginia’s 95 counties have passed such sanctuary measures opposing restrictions on the right to keep and bear arms. They suggest that the counties...