The FBI's National Instant Criminal Background Check System (NICS) vets millions of U.S. gun transactions every year. In order to function effectively, the system relies on state and local agencies as well as the military to report information such as mental illness or criminal convictions. This did not occur when a court-martialed Air Force veteran purchased a rifle in 2016 which he used to carry out a mass shooting at a church in Sutherland Springs, killing 25 people. That prompted Attorney General Jeff Sessions to order a review of NICS.
As can be seen from the following infographic, the number of background checks on U.S. firearm purchases is surging. This year, there were 203,086 checks for transactions on Good Friday alone, the largest single day volume since the system was created in 1998. In 2000, there were 8.5 million background checks and by the end of 2016, that had increased sharply to 27.5 million. Last year also saw a considerable increase in firearm retrievals. The FBI issued 4,170 orders to seize firearms from people who should have been prevented from buying them by the vetting system in 2016, up from 2,892 in 2015. That marks the largest increase in gun retrieval requests in 10 years and reasons for the orders include mental health issues or criminal convictions.