Was Scot Peterson, the sheriff’s deputy who didn’t storm into Marjory Stoneman Douglas High School in the midst of a mass shooting that claimed the lives of 17 teachers and students, a “coward,” as Donald Trump described him?

David Chipman, who, unlike Donald Trump, knows a thing or two about facing off against an armed gunman, says no—that Peterson is, instead, one of “the many victims of Parkland.” Chipman, a 25-year veteran of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), served on one of its Special Response Teams—the agency’s equivalent of SWAT—and is now a senior policy adviser to former congresswoman Gabrielle Giffords’s campaign to curb gun violence. He says, “We rightfully applaud heroes. People who disregard their own personal safety for another. But it is a rare act. We hope that when the chips are down, we will exercise our duty, but you never know until that day comes. I’d like to say I would have rushed into a building with only a handgun to confront an active shooter armed with a military-style assault rifle, knowing I was outgunned, knowing that I would likely die, but I don’t know.”

By all accounts, Scot Peterson had been a model cop until he became a national disgrace. “His personnel record is filled with commendations,” reported the Sun-Sentinel. “Four years ago, he was named school resource officer of the year. A year ago, a supervisor nominated him for Parkland deputy of the year.” But like most of us, he had never faced a situation like he did on the day that Nikolas Cruz shot 33 of his former classmates, teachers, and coaches with an AR-15.

The criticism Peterson’s received is understandable. He took a risky job. Since the school shooting at Columbine, police officers have been trained to enter a building in such circumstances, even if it might cost them their lives.

But Chipman says that the reality is that, even though they undergo extensive training designed to inoculate them against natural human stress reactions, it’s not uncommon for soldiers to freeze up the first time they experience combat. It’s not a sign of cowardice. In most cases, those same troops perform well—or even heroically—after that first exposure to real-life combat. We can’t expect police officers to behave any differently.

The data show that having access to a firearm almost doubles your risk of becoming a homicide victim, but, according to Pew, two-thirds of gun owners “cite protection as a major reason for owning a gun”—far more than any other reason given.

The gun lobby’s heroic-gunslinger fantasy also animates Donald Trump’s repeated calls for arming school teachers. It’s a distraction from the real issue—mass shootings, on and off campus, accounted for fewer than 4 percent of gun murders last year. Still, I asked Chipman: What’s wrong with the NRA’s idea that “good guys with guns” could stop people like Cruz? How realistic is it to expect a teacher, administrator, or other bystander to intervene in such a situation?

You can listen to our 20-minute interview through the player above, or read the transcript below, which has been edited for length and clarity.

Joshua Holland: We’ve had another mass shooting, and predictably, conservatives are calling for teachers to be armed. Conceding that we can’t post a police officer in every classroom, why shouldn’t we train teachers? Why not send them to the range, make sure that they’re proficient with their weapons, and hope that they can stop the next massacre?

David Chipman: Let me break it down a couple of ways. First, what the president really said is that the presence of guns in the hands of teachers would serve as a deterrent. Deterrence is something I believe in, and in policing, in certain respects, it does work. The problem is that [Nikolas Cruz] suffered from severe mental illness, and as we know, for most mass shooters, it’s basically a suicide attack, so that’s when deterrence falls apart. If you’re willing to die, it’s tough to imagine that a deterrent would work.

So let’s say that it isn’t a deterrent, but perhaps the outcome could be better. I was a trained SWAT team member for ATF. I was actually issued a semiautomatic AR-15 during my duty, so I know what that gun can do, and I know the type of training that I had not only to be proficient at shooting it, but also to be proficient when the chips were down.

I also have some expertise in teaching, because my father is a mathematics professor. Now, my dad and I are very different people. For instance, for his birthday, I gave him a device that caught bugs on the wall of his house so that he could let them go outside. This is a person who’s wired against killing anything, and I think that it’s interesting how people assume that everyone is capable of killing another human being, and the research shows that that’s just not true.

There’s this famous book called On Killing, by David Grossman, who studied how training in the military has evolved over the years. They used to qualify by shooting at round targets, and what they found is that once they got into combat, many of them did not fire their guns, and even when they fired their guns, they would purposely fire over the enemy. So they had to train people to actually shoot at targets that looked more like humans, and that’s why police qualify today on targets that aren’t round but are shaped like people.

So I think that unless you are trained—and you’re trained over and over again, and you practice like you play, which means you’re training in simulated life or death environments—the likelihood of you even firing your gun is small. And then the likelihood that you would actually hit a moving target surrounded by other moving targets—any trained operator knows the fallacy in that. It’s highly unlikely that it would turn out well.

Now, there’s a limited number of exceptions. The pro-gun people say this, “Well, what happens if you’re lined up against a wall and people are being slowly executed one at a time, would you want a gun?” Okay, sure, yeah, of course I would, but that’s not a realistic scenario we’re talking about.

JH: There’s a natural stress reaction that law enforcement and the military train hard to overcome. If you’re in a situation with an active shooter, you have adrenaline coursing through your body and that makes it very difficult to respond in an effective, smart manner. Can you talk about that a little bit?

DC: When you’re in a life-or-death encounter, your blood goes to your major organs and you experience tunnel vision. That’s why police and the military train repeatedly under similar conditions. I think that 30, 40 years ago, they would put you under stress by actually physically hurting you. They just exhausted us, because being very tired is similar to stress. We also trained in simulated situations where we were firing live ammo around each other, and there’s a difference in how you respond to a situation when you know you’re firing real bullets. It just changes everything.

I think you also have to understand the element of fear. The fear involved in doing these operations is something that every individual has to deal with on their own terms. Law enforcement doesn’t really provide much support in terms of how to deal with these things. Cops are really good at drinking together and telling stories, but they never really talk about what’s going on emotionally.

I’ve never talked about this before, but for me personally, to get through these operations, I would actually pretend that I was already dead. And in that way, I had the courage to do what I needed to do to safely to protect my team and do the operation. How many other people do that? I don’t know. I can just share my own experience. But I can just tell you that the movies and real life are so different, and it concerns me that we have a president talking about things that are way beyond his scope of qualifications.

JH: What’s the practical effect of coming down with tunnel vision?

DC: You lose your peripheral vision, and you only see what you’re focusing on. And the problem is that you become hyper-focused on that one target and you don’t see innocent victims nearby, or other offenders, or your partners who might be arriving on the scene. It’s a very dangerous thing that you can overcome through breathing and lots of practice. But you need to overcome it because it can put you in a situation where you not only don’t shoot your correct target, but you hit unintended people.

Yes, most [gun owners] practice, but they’re not practicing with rounds of ammunition zinging past their head.

JH: We should acknowledge that, as you said, there are situations in which it is proper for a bystander to intervene if he or she has a weapon, but for the most part, law enforcement counsels people not to do so in an active shooting situation unless they are immediately in front of the shooter and have a very clear shot. And then in that circumstance, you should put your weapon down immediately after firing. Why is that?

DC: Well, for a host of reasons. [Even] members of law enforcement are told not to shoot if they’re off-duty in a situation like that unless it’s a clear and imminent danger. They’re told that it’s better to be a good witness, because there have been so many incidents where off-duty officers are trying to render aid or defuse a situation, and they’re actually killed by law-enforcement [officers who think they’re the shooter].

That’s what happened to John Capano, the ATF agent most recently killed in the line of duty. It was New Year’s Eve [of 2011], he was going to a pharmacy to pick up a prescription for his father, and he walked into the middle of a prescription robbery. He engaged this robber, got into a fight with them, had his weapon drawn, and another off-duty cop shot and killed him.

Some aspects of law enforcement are like being a doctor. You never want to do harm. You don’t want to make the situation worse. And it seems to me that this idea of putting a gun in teachers’ hands is like giving up in this issue. The time that we needed to focus on the shooter in Florida was every moment prior to him exiting his Uber with a military-style assault rifle, and what I mean by that is all of the warning signs, how we regulate guns in America, his mental-health condition and what we could have done to intervene there. Those were the opportunities to be heroes and save the day—not after he began shooting, because we know that once the shots are fired, things move so quickly that even trained people have difficulty reacting fast enough to actually stop the shooting from occurring.

JH: It seems to me that we need a comprehensive approach, like we take for other public-health issues, but the discussion often gets derailed by either/or thinking. When you mention mental health, for example, people think that that means you’re trying to avoid the issue of banning assault weapons or other forms of gun control. What are some of the measures that the Giffords campaign is advocating right now?

DC: I love thinking about it in terms of that kind of culture of safety. I grew up just north of Detroit, so as a child I grew up riding in a car without seat belts, with both my parents smoking Pall Malls, and I think I was sitting over the gas tank. And here we are today, we have mandatory seat belt laws, we have airbags, and we have other sensors that help us drive safe, and it’s actually become cool to buy a safe car. Cars are marketed for their safety, and that has evolved over several decades.

At Giffords, I’m a concealed-carry owner, [Giffords co-founder] Mark Kelly is a combat war veteran—even Gabby [Giffords] has a naval warship filled with guns named after her. We are not anti-gun. We recognize how lethal guns can be in the wrong hands and how accidental shootings and other things can impact families in a bad way. So we want there to be more focus on smart technologies—different technologies that can make guns safer. From “smart guns” to visible signs that a gun is loaded, to just securing guns in your car. One of the biggest problems for law enforcement today is that as more people are carrying guns outside their home, they’re leaving them unsecured in cars and they get stolen and then those guns are used in crime. My boss in Detroit retired from ATF and within two years, he was walking his dog outside in northern Virginia and he was murdered with a gun by someone who had stolen it from a car two blocks away.

These are real things that happen to real people, and I think that people will do the right thing if it becomes the cultural norm. Like don’t drive drunk, that kind of thing. Unfortunately, the gun lobby sees safety as a potential mandate, and they just oppose any regulation or mandate whatsoever as a matter of principle, and so that’s what we’re up against. But I think the more we get cops like me and veterans and other gun owners saying, “Hey, look, I like my rights to have a gun, but I know how dangerous it is, and I want to make it safe,” I think we’re making progress.

JH: Another important piece of this is that the gun lobby pays lip-service to the idea of keeping guns out of the wrong hands, but they oppose every single measure to do so. An important component of this is not only closing the so-called gun-show loophole—which is not necessarily just about gun shows, it allows individuals to sell each other weapons without a background check—but also these red-flag laws that empower law enforcement to confiscate guns from people who are identified as a threat, at least on a temporary basis.

There are a number of things we could do that just seem like common sense. For example, there are mental illnesses that will disqualify you from purchasing a firearm, but when you’re given a 72-hour emergency hold during a moment of crisis, and a psychiatrist says you represent a threat to yourself and others, in most states there’s no mechanism for law enforcement to intervene in that circumstance and make sure that you don’t have guns.

So it’s not either/or, it’s yes/and. We need to improve these systems. We need to deal with the culture. And I believe that we should ban military-style weapons with high-capacity magazines that result in greater body counts.

Thank you for taking the time to speak with me, David. I really appreciate your expertise and wisdom on this topic.

DC: It’s always a pleasure.