When Zina Haughton obtained a restraining order that prohibited her physically abusive husband from purchasing a gun, she thought she was safe. But despite the court order, Mr. Haughton purchased a gun from an online private seller. Not long after, Mr. Haughton shot and murdered Zina and two of her colleagues. Unfortunately, stories like Zina’s are not foreign in cases of domestic abuse. Data shows that more than half of women murdered with guns in the United States are killed by intimate partners, and more than half of mass shootings are acts of domestic or family violence. A 2010 report by...