A new gun law has already prevented some potentially dangerous people from owning guns. But since that law was signed by President Joe Biden last summer, the number of mass shootings in the United States has only grown. Just this past week, three 9-year-olds and three adults were shot and killed at an elementary school in Nashville, Tennessee. The persistence of mass shootings in the United States highlights the limits of congressional action. The law didn't address many Democratic priorities for gun control, including universal background checks or the ban on so-called assault weapons that Biden has called for. For now, Congress appears to have returned to a familiar impasse.