Newtown, Connecticut. San Bernardino, California. Orlando, Florida. Las Vegas, Nevada. Sutherland Springs, Texas. Parkland, Florida. All these cities share a tragic history: Gunmen there used versions of the AR-15 semiautomatic rifle to commit some of the deadliest mass shootings in modern U.S. history.

Now, days after 17 people were shot to death at a Parkland, Florida, high school, the outcry against these AR-15s and other assault-style weapons has spiraled into a fever pitch. And while the country’s largest gun control advocacy groups moved away from pushing for a nationwide ban on such firearms long ago, the Parkland shooting has led one of the oldest and biggest organizations, the Brady Campaign to Prevent Gun Violence, to declare its support for an assault-style weapons ban.

“In the past, Brady has not been as outspoken on the assault weapon issue. We have, for years and years and years, been in support of an assault weapons ban, but we decided it really is time to put more attention on this tissue,” Brady’s Co-President Avery Gardiner said. “We can’t overlook that common thread in so many of these attacks, and it’s time to take action on this.”

While gun violence prevention groups certainly aren’t in favor of assault-style weapons, the fight for a federal ban on assault-style weapons ran out of most of its steam years ago. Not only do most conservative politicians consider the issue to be a dead end, but mass shootings using assault-style weapons are responsible for just a fraction of American gun violence, despite their widespread popularity.

The term “assault weapon” is nebulous, but state-level bans on such firearms have defined them as center-fire semi-automatic weapons that can take detachable magazines and have two or more features, like a specialized grip. Semi-automatic weapons require a trigger-pull to fire each bullet, but the chamber reloads automatically.

Up against the NRA’s deep pockets and decades-long head start, massive gun control advocacy groups like Brady, Giffords, and the Everytown for Gun Safety have largely focused on pushing for state-level gun control legislation while trying to shut down gun advocates’ bills in Congress. Neither Everytown, which didn’t respond to a request for comment this week, nor Giffords lists assault-style weapons among their top issues.

Instead, over the past year, their biggest priorities included strengthening background checks and state laws that keep guns out of the hands of convicted domestic abusers, as well as ensuring that Congress doesn’t pass bills to deregulate silencers or allow people to carry concealed firearms across state lines. And it worked: The proposals to make silencers easier to purchase and to allow for “concealed carry reciprocity” ultimately both failed to pass.

“We also believe that one gun in the hands of a dangerous person can do a lot of damage, regardless of what type of gun that is, so I think that’s why we were really focused on closing loopholes [in existing laws],” explained Robin Lloyd, director of government affairs for Giffords, a gun control advocacy group that was was launched in 2012 by former Arizona Rep. Gabby Giffords and astronaut Mark Kelly. Lloyd said the organization, one of the largest gun control advocacy groups in the country, has traditionally refrained from doing work around assault-style weapons.

Students take part in a "lie-in" on the road outside of the White House February 19, 2018 in Washington, DC , for three minutes at a time in an effort to symbolize the short amount of time it took alleged shooter Nikolas Cruz to gun down numerous people at Marjory Stoneman Douglas High School in Parkland, Fla., last week.Photo by Olivier Douliery/Abaca Press.

Statistically speaking, that approach is likely to save more lives. Just under 2 percent of people shot to death in 2013 died as a result of a mass shooting. Of the roughly 33,000 gun-related deaths that take place each year in the United States, almost two-thirds are suicides. Another 12,000 deaths are homicides, and the rest are mostly accidental fatalities.

A 2004 report to the Justice Department on the Federal Assault Weapons Ban also backs up that approach. If Congress renewed the legislation, which outlawed AR-15s in the U.S. from 1994 to 2004, its “effects on gun violence are likely to be small at best and perhaps too small for reliable measurement,” the report found.

Plus, for a long time, assault-style weapons like AR-15s were rarely used, even in mass shootings. Out of the 111 gun massacres — a shooting that causes the deaths of six or more people — that took place between 1966 and 2015, just 28 involved assault-style weapons, University of Massachusetts-Boston professor Louis Klarevas told VICE News last year. His book, “Rampage Nation: Securing America from Mass Shootings,” analyzed every gun massacre during that time period.

On the other hand, the 2004 report also warned that lifting the ban could flood the market with firearms that cause more injuries and fatalities than other types of guns. Sales of the AR-15 surged after the Federal Assault Weapons Ban ended, and Klarevas found that gun massacres have since skyrocketed. Versions of the AR-15 have recently become the weapon of choice for mass shooters: Six of the top 10 deadliest shootings in modern U.S. history used them. Five of those six shootings took place between 2015 and 2018.

Liberal legislators like California Sen. Dianne Feinstein have reintroduced proposals for an assault-style weapons ban in the 14 years since the first one lapsed, but they’ve never really gained traction among conservatives. Florida Gov. Rick Scott, however, announced on Friday that he now wants to raise the state’s minimum age to buy an assault rifle from 18 to 21. It’s a restriction that Florida Sen. Marco Rubio and President Donald Trump said they’d support on a national level.

“That’s a conversation we should be having,” the Brady Campaign’s Avery said, explaining that she’d also back the rule. “How do we want to be balancing those [laws]? Do we want 19-year-olds who have a history of emotional troubles to be able to buy an AR-15 when he couldn’t buy a handgun under federal law?” (Federally licensed firearms dealers are typically prohibited from selling handguns to people under 21.)

At the same time, Rubio sought to portray a nationwide ban on semi-automatic rifles as an idea few Americans truly believe in. “Banning all semi-auto weapons may have been popular with the audience at CNNTownHall,” he tweeted hours after the debate, which gathered Florida politicians, an NRA spokesperson, and a crowd of Parkland survivors to debate gun policy. “But it is a position well outside the mainstream.”

But 79 percent of Americans, including 70 percent of Republicans, support a ban on assault-style weapons, according to a 2017 NPR/Ipsos poll. And the more mass shootings the U.S. experiences, the stronger that support grows: In 2013, a year after 26 people were gunned down at Sandy Hook Elementary School in Newtown, Connecticut, the Pew Research Center found that only 55 percent of Americans support a ban on assault-style weapons.