A man who alleges an off-duty law enforcement officer held a gun to his head following a “road rage” incident has been given the go-ahead to pursue a Fourth Amendment claim.In a written opinion Friday, U.S. District Judge Robert M. Dow Jr. did not rule on the merits of Angel Marquez’s allegations against Demetrius Jackson, a police officer with the rank of lieutenant. Jackson is with the U.S. Department of Veterans Affairs.But Dow held Marquez had stated a claim that Jackson seized him and used excessive …