Pressure is mounting on Wall Street to do something about gun control.

Investment firms are reexamining their portfolios, dropping gun stocks, and asking weapons manufacturers what they are doing to make sure their products don't end up in a mass shooting.

This reevaluation comes as public anger over political inaction on gun control shifts toward the American companies that profit from gun sales.

It started with social media calls for companies — like Hertz, MetLife, and Delta — to end their partnerships with the National Rifle Association. Many of the companies targeted did.

Now Wall Street firms are coming under fire for investing retirement savings and pension funds in companies like American Outdoor Brands, which makes the AR-15 rifle used in the Parkland shooting. Last week, New Jersey lawmakers moved to restrict all state employee pension funds from investing in gun manufacturers. Joanne McCall, president of the Florida Education Association, is urging state lawmakers to do the same.

Shareholders at American Outdoor Brands, Dick’s Sporting Goods, and Sturm Ruger asked those companies to report on steps they’re taking to improve gun safety and mitigate gun violence. The requests were filed by religious groups linked to the Interfaith Center on Corporate Responsibility, which includes 300 institutional investors that manage $400 billion in assets, according to Bloomberg. (Dick’s Sporting Goods on Wednesday announced that it was ending sales of assault-style weapons at its stores.)

Meanwhile, reports that major 401(k) index funds run by Vanguard and TIAA-CREF have ownership stakes in the big three gunmakers have also prompted a social-media backlash:

Wall Street has noticed. The investment firm BlackRock, which owns the largest stake in American Outdoor Brands and Sturm Ruger, said it has reached out to gun industry executives to see what they plan to do about gun violence. Blackstone Group, another Wall Street investment firm, sent an email to fund managers over the weekend, asking them whether they have any stakes in the gun manufacturers.

Other investment firms are renewing efforts to keep gun stocks out of their portfolio — efforts that have been building since the Sandy Hook massacre.

The movement is the latest example of American voters channeling their frustration into consumer boycotts when political action fails.

How Sandy Hook-inspired gun divestment

Pressure has been building in recent years for Wall Street firms to dump gun stocks — ever since the Newtown, Connecticut, shooting that killed 20 children in 2012.

Put simply, divestment is when an organization or individual sells shares of stock in a given company or sector. Activists have been using divestment as a political strategy for decades — as far back as apartheid-era South Africa. Since then, divestment has become a grassroots movement to urge ordinary consumers to invest their retirement savings in ethical ways, and even to use them as vehicles for political change, such as with the divestment movement targeting fossil fuels.

It was considered an effective strategy in apartheid South Africa. Opponents of the apartheid regime focused their ire on the companies that were directly invested in the country. They began urging institutional investors, including universities, to divest their assets from companies that did business with the regime. Archbishop Desmond Tutu credited the divestment campaign as a key tactic in bringing down apartheid.

The concept of divesting became mainstream in the United States during the climate change debate. Frustration over what was viewed as weak UN climate agreements, plus the US Senate's failure to pass a climate bill in 2010, pushed foundations and nonprofit groups —such as Greenpeace — to ensure their investments were not going to big oil companies.

Activist celebrities, like Leonardo DiCaprio, popularized the idea, encouraging Americans to make sure their retirement money was invested in renewable energy. In 2015, a group of foundations launched the DivestInvest initiative, which helps foundations, individuals and businesses divest from fossil fuels.

In recent years, gun-control activists have turned to divestiture as a tactic. Rapper Snoop Dogg and angel investor Ron Conway joined the Campaign to Unload, launched in the wake of Sandy Hook and featuring the hashtag #UnloadYour401k.

In 2016, two tech workers created Goodbye Gun Stocks, a web app that allowed users to see if their 401(k) savings were invested in gun stocks. One of the creators, Keywon Chung, said she was inspired to take the idea of fossil-fuel divestitures to the gun debate.

Asset managers say that more and more Americans have been adamant about restricting firearms companies from these funds. And it’s having an impact.

According to a 2016 US SIF: The Forum for Sustainable and Responsible Investment report, some $845 billion in assets were affected by divestment targeting military contractors and weapons makers. That's a jump of about 1,042 percent since the Sandy Hook school shooting in December 2012. (Only $74 billion in institutional investments restricted guns at the beginning of 2012.)

Calls to divest from Remington, which made the AR-15 used in Sandy Hook, are one factor that pushed the company into bankruptcy. Cerberus, the investment firm that owned the largest stake in the company, told Bloomberg that it decided to sell the company "amid pressure from investors revolted by the carnage" in Sandy Hook.

Gun manufacturers were already struggling

Business was bad for gun makers even before the latest mass shooting.

Remington announced its bankruptcy on February 12 — two days before the massacre in Parkland.

Stocks began to tumble for American Outdoor Brands the day after the Parkland shooter killed 17 people at Marjory Stoneman Douglas High School, following reports that the weapon used in the shooting was an AR-15 made by the Massachusetts-based company, formerly known as Smith & Wesson.

Since then, the company's stocks have dropped about 12.5 percent. Stock prices for the other two big gun makers have dropped too.

Gun companies had been struggling ever since Trump won the presidential election. Gun sales normally spike when Democrats are in power, as gun owners’ fears of gun-control measures rise. With Trump in power, sales have fallen.

Stock prices for gun manufacturers also tend to rise after mass shootings, likely because the debate over gun control heats up and rekindles fears from gun owners. For example, stock prices for American Outdoor Brands spiked in the week following the 2016 shooting that killed 49 people at a nightclub in Orlando, and again after the October shooting that killed 58 people at a Las Vegas concert.

Reaction to the Parkland shooting seems different. Renewed calls for gun control haven't had the effect of boosting gun stock prices. In fact, they continue to fall.