Each year, an estimated 33,636 people die in the United States from gunfire. The victims mainly die by suicide, but also from the high rates of gun violence and gun accidents in the U.S. compared to other developed countries. Since 1968, 1.5 million Americans — more than all the dead from all the wars in U.S. history — have perished after being shot.

But since the mid-1990s, the federal government has done exceptionally little to investigate the threat posed by firearms, thanks largely to successful efforts by the National Rifle Association to intimidate, threaten and harass the Centers for Disease Control and Prevention, the National Institutes of Health and other federal agencies.

MSNBC reports that after a 1993 CDC-funded study found that firearm ownership significantly raised the risk of homicide in homes, the NRA's Republican allies in Congress moved to cut off funding for the CDC's National Center for Injury Prevention and Control in 1994. That effort failed, but in 1996, Congress reallocated the $2.6 million from the NCIPC's budget that was devoted for gun research and prohibited the CDC from allocating any of its funds "to advocate or promote gun control." The CDC, fearing further budget cuts, enacted a self-imposed ban on any research related to firearms.

In 2003, Congress also successfully prohibited the Bureau of Alcohol, Tobacco and Firearms from releasing tracking information about guns used in crimes to the public, creating another high barrier to research.

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Follow the money: "I think that the NRA exists to help sell more guns," Mark Rosenberg, who became the first director of the NCIPC in 1994 and served until 1999, told Mic in a phone interview. "I think that the leadership of the NRA saw what some of our early research was showing. The NRA wanted people to feel that the best way to protect your family in your home was to have a gun. And they thought that was a good way to sell guns."

"They decided they needed to shut this research down," he said.

Shut it down they did. Over the last 40 years, MSNBC reports the NIH funded just three studies on gun violence, while the CDC now "asks researchers to let it know any time they're publishing something on firearms — then gives the NRA a heads up."

"They're the ones who have exactly the resources that are needed," Elliot Fineman, founder of the National Gun Victims Action Council, told Mic in a phone interview. "We're living under a gun violence epidemic. We all know that. Think of the response they have when they find out cans of tomato soup are poisoning people. They recall millions of cans of tomato soup. The full mechanisms of the government come into play."

"In a nation dedicated to personal freedom and responsibility, it is ironic that policymakers and the public have been denied access to timely and objective research on this issue for 15 years and counting," researcher Arthur Kellermann, who contributed to the original controversial study, told Salon in 2012.

President Barack Obama ordered the CDC to resume studying gun violence in the wake of the 2012 massacre at Sandy Hook Elementary School, but the agency still lacks funding to do the research.

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As a result, people are dying needlessly: Most gun owners say they own guns for self-defense, and that owning a gun makes them feel safer. The NRA happily promotes this narrative, despite the fact that subsequent research has reinforced the CDC's initial findings that guns in the home increase the chance of homicide and suicide.

One 2004 study concluded "persons with guns in the home, regardless of the type of gun, number of guns, or storage practice, were at significantly greater risk of dying from a firearm homicide and firearm suicide than those without guns in the home." In 2014, University of California San Francisco researchers compiled 15 separate studies on gun violence and discovered people with access to firearms are three times as likely to commit suicide and nearly twice as likely to become a homicide victim.

Research by behavioral scientist Jeffrey Swanson released earlier this year suggests a clear correlation between dangerous personality traits and ownership of multiple guns. According to Pacific Standard, Swanson estimated 8,865 out of every 100,000 Americans both owns a gun and engages in behavior like "angry outbursts, smashing things in anger or losing their temper and engaging in physical fights."

Rosenberg, the former NCIPC director, told Mic he believes that such risk factors could be more thoroughly studied with adequate research and evidence-based public policy, but the NRA's "zero-tolerance" stance shut down scientific inquiry at the only national research body capable of identifying what could be done about gun violence.

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"There are very big questions about basic policies like gun registration," Rosenberg said. "Where and when people can carry and use guns, how to address the problem of finding high risk potential purchasers before they purchase. These are all big questions that still need to be answered. Absolutely the best time to have started this research was 20 years ago."

Frustratingly, many of the steps being blocked by the NRA's stance on gun research might not even require gun control.

"It's not either/or," said Rosenberg. "We made cars safer and there are more cars on the road than ever before. It's exactly the same we can do with guns, but we can't do it without the studies."

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"It's no longer acceptable for people to say, 'Well, what can we do. There's nothing to be done,'" Fineman said. "We're not going to get zero shootings, we're not going to get zero drunk drivers. But we can minimize the gun violence epidemic."

"Imagine we had an epidemic that was killing people and we had no idea what it was," he told Mic. The president would "immediately charge the CDC with doing the research to find out what needs to be done."