Former Pennsylvania Sen. Rick Santorum holds an AR-15 assault rifle at a shooting range during his presidential campaign on January 30, 2016. Brian Frank/Reuters 
 
 Over the weekend, Rick Santorum, a former Pennsylvania senator and Republican who previously ran for president, suggested that student protestors should learn CPR instead of pushing for stricter gun control laws. Now he's walking back the statement. 
 
 "How about kids — instead of looking to someone else to solve their problem — do something about maybe taking CPR classes or trying to deal with situations that, when there is a violent shooter, that you can actually respond to that?" Santorum, who is also a CNN commentator, said during a Sunday broadcast of the network's show "State of the Union." 
 
 On Wednesday, Santorum told CNN, "I did misspeak in using the term CPR." He also noted that gun control advocacy has helped bolster "organizations and people who have actually focused on what we can do ... to actually prevent these types of things." 
 
 Santorum made his original remarks over the weekend while roughly two million people at hundreds of "March for Our Lives" events across the US rallied against gun violence in America. 
 
 The student-led protests commenced after 17 people were shot to death at Marjory Stoneman Douglas High School. In the February 14 mass shooting in Parkland, Florida, a 19-year-old former student is believed to have committed the murders using a legally purchased AR-15 assault rifle. 
 
 David Hogg, a survivor of that school shooting and a "March for Our Lives" organizer, responded to Santorum's remarks in a broadcast on CNN. 
 
 "There are many programs that work to ensure, especially in communities that are heavily affected by gun violence, [...] that students are able to respond and administer whatever first aid they can, assuming the person is still alive," Hogg said on Sunday. "But at the end of the day, if you take a bullet from an AR-15 to the head, no amount of CPR is going to save you because you're dead." 
 
 Medical doctors on Twitter joined Hogg's criticism of Santorum's remarks, noting that CPR is often futile following gunshot wounds. 
 
 "Gobsmackingly uninformed," tweeted Dr. Heather Sher, a radiologist in Florida. "CPR is not effective with catastrophic bleeding." 
 
 Joseph Sakran, a trauma surgeon at Johns Hopkins Medicine and self-described gun violence survivor, tweeted: "Victims that go into cardiac arrest after #GunViolence are Bleeding to Death. CPR is NOT effective in this situation." 
 
 Santorum did not immediately respond to Business Insider's request for comment. 
 
 Why gunshot wounds can be so damaging that CPR doesn't work 
 
 Ballistic gelatin is a model for how soft tissues respond to gunshot wounds. Nathan Boor & Kurt Groover/Aimed Research/Wikimedia Commons 
 
 To humanely probe the physics of gunshot wounds, and ultimately help police solve crimes and doctors save lives, researchers shoot bullets into inert, flesh-like substances. 
 
 In many cases, they use a large block of synthetic gelatin and water to simulate the impact of a speeding bullet on human tissue. 
 
 Here's an example from the YouTube channel EffectiveAffect of what a gunshot simulation in gelatin looks like. This bullet was moving at about 2,900 feet per second through 575 cubic inches of gelatin. 
 
 Many factors determine how damaging bullet wounds can be. The type of gun and bullet used, the range of the shot, where on the body a person was shot, and whether or not the bullet exited the body afterward all make a difference. 
 
 But some basic principles remain: When a bullet is traveling at supersonic speeds, it partially slows down the moment it hits a person. The energy of the blast needs to go somewhere, so it radiates outward from the bullet's path to the surrounding tissues. This creates a much larger "mushrooming" effect, which you can see above. 
 
 This temporary ballooning of tissue is actually what causes the most damage, according to a post on Mongabay.com. The billowing flesh lacerates blood vessels and surrounding organs, tissues, and bone. 
 
 The Washington Post reported in June 2017 that this shockwave can leave a track of wounding as much as "five to 10 times wider than the bullet." 
 
 Gelatin isn't a perfect proxy for the human body. We have bones and cartilage, which can skew the bullet's path, sending it into a tailspin that could cause it to break apart and get lodged in different spaces, further complicating the severity of the wound. 
 
 This why an increasing number of researchers are turning to advanced computer simulations. Such models can recreate the complex layers of tissue in the human body to study a practically infinite number of grievous wounds from all angles, speeds, and styles of bullets (or even shrapnel from mines and improvised explosive devices). 
 
 A model that debuted in 2015, for example, simulated a human leg, its skin, muscle, bone, large arteries, and even small veins. Then it applied the physics of fluid dynamics to explore the origins of traumatic blood loss, and the best methods to stop that bleeding. 
 
 But as Alex Ossola reported for Popular Science, this and other models aren't perfect — so there's still a lot left for scientists and doctors to learn. This makes gunshot wounds as enigmatic as they are damaging and dangerous. 
 
 Julia Calderone and David Choi contributed to this post. ||||| Doctors are firing back on Twitter over Rick Santorum’s suggestion that students take “CPR classes” instead of advocating for gun control following last month’s massacre in Parkland, Florida. 
 
 Hundreds of thousands of people, including students from throughout the nation, marched on Washington on Saturday, demanding lawmakers pass stricter gun laws after 17 people were shot to death Feb. 14 at Marjory Stoneman Douglas High School. Similar demonstrations occurred in other U.S. cities and across the world. 
 
 On Sunday, Santorum accused students of trying to pass the buck when it came to keeping their schools safe. 
 
 “How about kids, instead of looking to someone else to solve their problem, do something about maybe taking CPR classes or trying to deal with situations where there is a violent shooter,” Santorum, a former Republican senator from Pennsylvania and CNN political commentator, said on the cable news network. 
 
 His comments drew backlash on social media from doctors, including Eugene Gu, a third-year general surgery resident at Vanderbilt hospital in Nashville, Tennessee. ||||| Rick Santorum’s comment suggesting that school shooting survivors learn CPR came one day after thousands gathered across the country for March for Our Lives rallies. | Darren McCollester/Getty Images Santorum on CPR comments: I misspoke 
 
 CNN commentator Rick Santorum said Wednesday that he misspoke last Sunday when he said survivors of a school shooting in Parkland, Florida, should have taken CPR classes in response to the attack instead of “looking to someone else to solve their problem.” 
 
 “The fact of the matter is I did misspeak in using the term CPR and I think Sanjay Gupta’s job here at CNN is probably safe as being the medical commentator on things,” Santorum, a former Republican senator and presidential candidate, said on CNN’s “New Day.” 
 
 Story Continued Below 
 
 Santorum’s initial comment suggesting that school shooting survivors learn CPR came one day after thousands gathered in Washington and in cities across the country for March for Our Lives rallies calling for stricter gun control laws. Those rallies were prompted by last month’s shooting at Marjory Stoneman Douglas High School, where a gunman killed 17 people. 
 
 Santorum was widely rebuked for his CPR comments. Students who lived through the shooting, and even doctors, weighed in publicly, telling the former senator that CPR would not have saved the lives of the victims. 
 
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 Santorum said his comment about CPR “obscured the larger point” that past mass shootings have spawned organizations that he said have done significant work in combating school shootings by addressing mental health issues and bullying. Calls for divisive steps to impose stricter gun control laws obscure the work that such organizations do, Santorum said. 
 
 “What I’ve seen happen here is avoiding the issues that are really actually unifying,” he continued. “I mean, that's really the most disturbing thing.”
– Former GOP presidential candidate Rick Santorum thinks students should learn CPR instead of "looking to someone else to solve their problem" by protesting gun violence—and a lot of doctors think Santorum should get a clue. His remarks were slammed by numerous medical professionals on social media, many of whom pointed out that CPR generally isn't enough to save people shot with AR-15-style rifles like the one used in the Parkland mass shooting, the Huffington Post reports. "I've operated on gunshot victims who've had bullets tear through their intestines, cut through their spinal cord, and pulverize their kidneys and liver," tweeted Eugene Gu, a surgeon at a Nashville hospital. "Rick Santorum telling kids to shut up and take CPR classes is simply unconscionable." Santorum was also criticized by California's Rep. Ted Lieu. "CPR is good for heart stoppage. Not good for victims of multiple AR-15 bullets, which typically impart 3 times the lethal energy upon impact than a 9mm handgun bullet," the Democrat tweeted. "AR-15 bullets obliterate organs and cause so much bleeding that victims die very quickly." Santorum made his remarks on CNN on Sunday, the day after protesters demanded tighter gun laws at March for Our Lives rallies in Washington, DC, and across the US. He said students should learn CPR or learn "to deal with situations" where they could respond to a shooter instead of seeking "phony gun laws." (This was one of the DC rally's most gripping moments.)