America's biggest gun lobby to hold meeting after mass shooting

In the United States, the National Rifle Association meets three days after 19 children and two teachers were killed at an elementary school in Texas. The tragedy is the deadliest school shooting since the Sandy Hook massacre, which killed 27 in 2012. What is the NRA, why does it wield so much influence on American politics, and how can the group continue to oppose changes to gun laws despite multiple mass shootings?