The attack on former President Donald Trump, which the Federal Bureau of Investigation is probing as a “potential domestic terrorism act,” was both an assassination attempt and a mass shooting — defined as four or more victims shot, per the Gun Violence Archive. It was one of nearly 300 mass shootings that have transpired in the United States so far this year. 

A shooter opened fire at a rally for Trump in Butler, Pennsylvania, on July 13, killing an attendee and wounding the former president and three others. The shooter, who’d fired from a rooftop roughly 500 feet away, was killed by a Secret Service sniper.

Here’s what else we know:

The victim and survivors have been identified

Corey Comperatore, 50, died shielding his family from gunfire. Comperatore was the former chief of the Buffalo Township Volunteer Fire Company in Sarver, Pennsylvania, where he lived with his wife and two daughters. He was “so excited” to attend the rally, said Pennsylvania Governor Josh Shapiro, who called him a “hero.” The injured rally attendees were David Dutch, 57, of New Kensington, and James Copenhaver, 74, of Moon Township. U.S. Representative Ronny Jackson of Texas said his nephew was also injured, having been grazed in the neck by a bullet, and was treated at the scene; he has not been publicly named.

The shooter’s motives are unclear

The 20-year-old shooter was a resident of Bethel Park, a suburb of Pittsburgh, and worked as an aide in a nursing home. The FBI said he appears to have acted alone. He did not have a criminal or mental health history. Details have emerged about his possible political leanings, but they’re contradictory: He was a registered Republican who last voted in the 2022 midterms, according to voting records, but someone with the same name and zip code also donated $15 to the Progressive Turnout Project, a liberal get-out-the-vote organization, in 2021. The shooter was wearing a T-shirt with the logo of Demolition Ranch, a YouTube channel run by a gun enthusiast, per photos from the scene. According to former classmates, he espoused conservative views.

The gun belonged to the shooter’s father

The AR-style rifle was legally purchased by the shooter’s father in 2013, according to an ATF trace. After the attack, the father said he was trying to figure out “what the hell is going on,” but he is reportedly cooperating with investigators. Materials that could be used to make explosive devices were found inside the shooter’s car.

The Secret Service is facing questions over a “massive security breach”

Lawmakers from both sides of the aisle have deemed Saturday’s shooting a security failure and questioned how an assassination attempt could be carried out under the nose of the Secret Service. House Republicans are planning hearings next week to interrogate the head of the agency. Questions are also being raised about the response: Several attendees pointed out the shooter to police before the shooting, and the Associated Press reported that an officer encountered the shooter on the rooftop before he opened fire but retreated without engaging him.

Experts had warned of political violence around the 2024 election

A Department of Homeland Security analysis in February warned that “threat actors intent on harming Americans through the use of violence may become more aggressive as Election Day approaches.” Garen Wintemute, head of the California Firearm Violence Research Center at the University of California, Davis, has been conducting extensive surveys around Americans’ willingness to engage in political violence, and reported last year that a third of respondents believed violence was justified to advance political objectives.

Republican lawmakers engaged in inflammatory rhetoric — amid calls to tone it down

U.S. Representative Marjorie Taylor Greene of Georgia posted on X, formerly Twitter, that Democrats “tried to murder President Trump.” U.S. Representative Mike Collins, also from Georgia, posted that charges should be filed against President Joe Biden “for inciting an assassination.” Mississippi Governor Phil Bryant blamed the assassination attempt on Trump’s political opponents and the law enforcement officials trying to hold the former president to account. Florida Senator Rick Scott implicated “Democrats and liberals in the media.” Ohio Senator J.D. Vance blamed the Biden campaign’s “rhetoric.” Critics pointed to Republicans’ history of violent rhetoric. During his flight to the Republican National Convention on Sunday, Trump said the attack changed his campaign and that he’d “love to achieve unity if you could achieve unity,” but questioned if that was possible. In an Oval Office address, Biden implored Americans to “lower the temperature.”

All eyes turn to the Republican National Convention — where guns can’t be banned

The Trump rally shooter staged his attack from outside the Secret Service’s security perimeter. Although Wisconsin Governor Tony Evers, a Democrat, asked the agency to further restrict guns near the convention, law enforcement officials on Sunday said they would not be increasing security for the Milwaukee convention. However, CBS reported that law enforcement officials plan to create buffer zones around the events. Guns will be allowed in the area outside the Secret Service’s credentials-only hard security zone, known as the “soft perimeter.” State law prevents the city from banning most firearms.

Sunny Sone contributed to this story.