In less than a week, the United States has seen two deadly mass shootings: one in Boulder, Colo., and another in the Atlanta area. These events prompted President Biden to address the nation on Tuesday. In his speech, he said it was time to ban assault weapons. Mr. Biden has been here before. He has tried several times in his political career to bring in gun-control legislation, all to little avail. How likely is this latest attempt to succeed, and what lessons can Mr. Biden take from his decades-long effort?