Last week Sen. Dianne Feinstein introduced a new version of the federal "assault weapon" ban that expired in 2004. Like that earlier law, notes Senior Editor Jacob Sullum, Feinstein's bill prohibits the manufacture and sale of guns based on characteristics that have little or nothing to do with the danger they pose. Sullum says new survey data suggest why most Americans nevertheless want to ban "assault weapons": Most Americans don't know what "assault weapons" are.