Preventing medical marijuana card holders from obtaining firearms does not violate the Second Amendment, a federal court of appeals said Wednesday, rejecting a challenge to a federal ban preventing card holders from purchasing firearms. The case stemmed from a lawsuit filed by Nevada resident S. Rowan Wilson after she was turned away by a firearms dealer who knew she had a medical marijuana card. Ms. Wilson, who says she obtained the card as a sign of support for legalizing marijuana, but does not use it herself, challenged a directive from the Bureau of Alcohol, Tobacco, Firearms and Explosives instructing dealers not to sell firearms to card holders.