In April, Donald Trump became the first president in a quarter-century to speak at the National Rifle Association (NRA) annual convention, a sign that his views on guns align with those of the powerful gun lobby. While federal courts in late 2016 and early 2017 dealt blows to gun-rights proponents, a Republican-led Congress and the White House this year have begun rolling back Obama-era firearms restrictions. Several states are considering loosening gun-control policies, and two have enacted laws allowing residents to carry concealed firearms without first obtaining a permit or training. In Connecticut, families of some of the two dozen victims of the December 2012 Sandy Hook Elementary School massacre continue to pursue legal action against the maker of the gun used by the shooter.

First responders secure the area outside the Fort Lauderdale-Hollywood International Airport in Florida after a shooting near the baggage claim area on Jan. 6, 2017. Five tourists were killed in the attack by a single gunman. (Getty Images/Joe Raedle)

Mass shootings — those in which at least four people are killed — continued to make headlines in the United States during the past year.

The first six months of 2017 saw 174 mass shootings. 1 In January, a 26-year-old man shot 11 people, five fatally, at an airport in Fort Lauderdale, Fla. Two months later, two men at a Cincinnati nightclub shot 17 people, killing one. 2