A familiar icon lies behind Trump’s attempted assassination: the AR-15

The gun’s popular qualities—a lightweight profile, easy handling and ability to shoot lots of bullets quickly—have made it a blockbuster. The number of ARs in civilian hands rose from 400,000 in the early 1990s to more than 20 million by the 2020s.

Those same qualities have also made it easy for disturbed people and political extremists to wreak havoc in mass shootings at schools, movie theaters, concerts, government offices, grocery stores—anywhere Americans gather.

Until Saturday, though, the AR-15 had never been used to try to assassinate someone who has served as the U.S. president. And that former president has given his political support to ensuring that the AR-15 remains legal.

“The more this type of weaponry becomes popular in the American public, the more likely it’s going to be used in that context," said James Densley, a criminology professor and co-founder of the Violence Project, which tracks mass shootings.

Though the AR-15 wasn’t designed to kill from far away, the shooter on Saturday was within range to hit the former president, not much more than a football field away, a law-enforcement official said. Trump, who was giving a campaign speech, later said he felt one of the bullets rip through his ear. One Trump supporter was killed and two others were critically injured.

A new urgency

Designed in the 1950s, the gun broke from the longstanding tradition of military rifles crafted for marksmen to shoot accurately at great distances. Instead, it responded to military officials’ desire for a weapon that could unleash a high volume of lead at close range, countering guerrillas armed with durable, rapid-fire Soviet AK-47s.

Cultural and political shifts over the past three decades have transformed the civilian version of the gun from a niche product to a mass-market phenomenon. Today, the AR-15 has become the indelible icon of the nation’s prolonged argument over the role of guns in society. Millions of gun owners embrace the rifle as the symbol of Second Amendment rights. Opponents see it as a symbol of gun culture run amok, the weapon of choice for extremists and mass shooters.

It also has long been intertwined with presidential politics. Sales of the weapon have fluctuated widely based on who holds the presidency. AR-15 makers have for years linked production to political events and mass shootings, a phenomenon that industry executives call “fear-based buying."

Now the debate over the gun has reached a new urgency and intensity.

On Sunday, gun-control activists seized on the idea that a man armed with an AR-15 almost got to one of the world’s most protected leaders.

Kris Brown, president of Brady, a gun-control group, pointed to the efforts by her group’s namesake, Jim Brady, to pass tighter gun laws after he was shot in a 1981 assassination attempt while working as President Reagan’s press secretary.

“We can only hope that the events of today will have the same impact and inspire calls of action," she said.

On a warm Saturday night at a fairground in Butler, Pa., where Trump took the stage to the Lee Greenwood anthem, “God Bless the U.S.A.," a 20-year-old man allegedly fired an AR-15 from a rooftop just outside the rally.

The suspected gunman, Thomas Matthew Crooks, was killed by a Secret Service sniper. Authorities are probing the man’s motive. Crooks used an AR-15 purchased by his father, The Wall Street Journal reported.

Depending on its design, an AR-15 can be accurate to around 600 yards and fires a small .223 or 5.56-caliber bullet. Versions of the rifle are sold at gun stores everywhere with prices ranging from a couple hundred dollars to several thousand. A shooter’s accuracy with an AR-15 can be affected by a number of factors from the wind to whether the rifle was equipped with an optic.

Easy to shoot

Eugene Stoner, a self-taught gun designer, created the AR-15 for the U.S. military in the 1950s at ArmaLite, a small company in Southern California. The weapon’s revolutionary design made it lightweight and easy to shoot. Stoner used modern materials like aluminum and plastic instead of heavy wood and steel. He devised an ingenious way of using the hot gas from the exploding gunpowder to move parts inside the gun to eject spent casings and load new rounds. It was ArmaLite’s 15th creation, hence the name.

American officials wanted a gun that fired small-caliber bullets so soldiers could carry lots of ammunition, but these bullets still needed enough power to pierce a steel helmet at 500 yards. Stoner designed a small round that flew through the air at a high velocity. When the bullets hit the human body, they became unstable quickly and carved through organs and bone like tornadoes.

The rifle, renamed the M16 by the military, could fire either in full automatic mode, meaning the shooter unleashed a stream of bullets by pulling the trigger once, or semiautomatic, meaning the shooter fired one round per trigger pull. The military ramped up production for the war in Vietnam but made ill-informed design changes that caused the rifle to fail miserably on the battlefield early on. Soldiers died with jammed M16s in their hands, leading to public outcry and congressional hearings.

From the early 1960s, Colt sought to sell a semiautomatic version of the rifle as “a superb hunting partner" to civilians. But most hunters preferred rifles made of polished wood and steel, not aluminum and plastic. The ability to shoot lots of bullets quickly wasn’t a big draw to sportsmen who prided themselves on accuracy.

The jump to mass market

The federal assault-weapons ban in 1994 helped propel the gun’s popularity. Backed by Democratic President Bill Clinton and then-Sen. Joe Biden, the ban transformed the gun into a potent symbol of Second Amendment rights.

After the Sept. 11 attacks, the gun’s appeal broadened with veterans who used the military version in Iraq and Afghanistan and with the wider public. The expiration of the federal assault-weapons ban in 2004 and the passage of legislation to protect gun makers from lawsuits combined to create an ideal environment for large gun makers to manufacture, market and sell large quantities of AR-15s.

Americans who bought the rifle liked how easy it was to shoot and keep on target with its light recoil. The unique design made it easy to swap parts, earning the gun the nickname “Legos for adults."

Politics and threats of bans supercharged the market for the AR-15. New efforts by gun makers to promote their products in popular videogames added to the AR-15’s widespread recognition.

The gun’s rise coincided with a sinister trend. Over the coming years, the AR-15 would grab national headlines as a weapon of choice for mass shooters, with their locations now well-known to the American public: a movie theater in Aurora, Colo., an elementary school in Sandy Hook, Conn., a high school in Parkland, Fla., a supermarket in Buffalo, N.Y., an elementary school in Uvalde, Texas, and many more.

Almost all took place at close range. An exception was the deadliest mass shooting in American history. In 2017, a gunman perched high in a Las Vegas hotel used AR-15 rifles to fire on a crowd of concertgoers more than 400 yards away, killing 58 that day and wounding hundreds more.

Trump Slump

When Trump ran for office in 2016, some gun-owners were skeptical because years earlier he had written in a book that he supported the federal assault-weapons ban. He eased those concerns by blasting the plan of his opponent, Democrat Hillary Clinton, to ban AR-15s and winning the backing of the National Rifle Association.

“Gun-banners are unfortunately preoccupied with the AR-15, magazine capacity, grips, and other aesthetics precisely because of its popularity," Trump said in an interview with a gun blog.

Gun makers supported Trump, but ramped up AR-15 production in anticipation of a Clinton victory. When Trump won, sales plummeted as gun owners no longer feared a ban was imminent. Gun makers dubbed the era “the Trump Slump," with many laying off workers and some declaring bankruptcy.

Major mass shootings with AR-15s and a growing youth movement for stricter gun laws put pressure on Trump to take action. He held meetings with Democratic leaders and agreed to look into the issue, but stood firm with his gun-rights allies in the end. His administration did impose a ban on “bump stocks," devices used by the Las Vegas shooter to make his AR-15s mimic automatic fire. The U.S. Supreme Court last month struck down that ban.

The gun retained a prominent place in American politics throughout Trump’s presidency—with Democrats calling for the rifle’s sale to be banned. In 2019, then Democratic presidential candidate Beto O’Rourke famously said during a debate, “Hell yes, we’re going to take your AR-15."

Republicans argued owning such a rapid-fire rifle was an inherent right of American citizens. Gun-rights supporters touted AR-15 ownership. A common flag today bears a silhouette of the gun and the phrase, “Come and Take It."

In early 2020, a smiling Donald Trump Jr. posted a photo of himself on Instagram holding an AR-15 with a magazine that bore an image of Hillary Clinton behind bars.

About a year later, members of a crowd outside the Capitol waved banners with images of the rifle before many there stormed Congress. In a nearby hotel, followers of the extremist group the Oath Keepers had stored AR-15s and ammunition in anticipation of an uprising, according to federal authorities.

In 2020, another extremist group also trained with AR-15s in a plot to kidnap Michigan’s Democratic Gov. Gretchen Whitmer. The same year, yet another group trained with AR-15s for a planned attack on a gun rally in Richmond, Va., to spark social unrest. Both plots were foiled.

In recent years, the stalemate over the AR-15 has hardened. Democratic-led states have imposed bans; Republican-led states have loosened restrictions and the courts have been flooded with cases pertaining to guns, including the AR-15. Sales of the gun surged during the pandemic, social unrest, and after mass shootings.

Biden has pushed strongly to pass a federal assault-weapons ban similar to the one that he helped pass as a senator. Key Republican leaders have opposed such efforts.

The endless debate over what to do about the AR-15—the rifle Americans love to love or love to hate—had been relatively quiet for much of this election cycle.

Until Saturday.

Write to Zusha Elinson at zusha.elinson@wsj.com and Cameron McWhirter at Cameron.McWhirter@wsj.com

Zusha Elinson and Cameron McWhirter are reporters for The Wall Street Journal and co-authors of “American Gun: The True Story of the AR-15," published by Farrar, Straus and Giroux.