2020 saw a historic rise in homicides in the U.S. - the vast majority committed with a gun - and the upward trend is continuing in 2021.
Why it matters: The murder surge represents a sharp break from decades of reductions in violent, gun-driven crime in the U.S., and experts are divided on what caused the increase - and therefore, what to do about it.
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Curbing the rise in shootings will require addressing the root causes of violence, while mending social trust between the communities most at risk and the police.
What we're hearing: Both political parties recognize the issue's power.
John Feinblatt - president of Everytown for Gun Safety, which calls itself America's largest gun violence prevention organization - tells Axios: "As a political issue, gun safety helped elected gun-sense majorities in both houses of Congress and the White House, and will only grow in its power as we seek to send gun lobby allies packing."
By the numbers: Provisional data from the Centers for Disease Control's National Center for Health Statistics released earlier this month indicates that the murder rate rose 30% between 2019 and 2020.
That's the highest increase in recorded history. Only the 20% spike between 2000 and 2001 comes close, and that's chiefly due to the nearly 3,000 people killed in the 9/11 attacks.
Murders are still rising in 2021, though at a slower pace: Data from Jeff Asher at AH Datalytics indicates that homicides in 91 big cities are up 9.1% year to date, with fewer than 35% of cities recording a drop from 2020 so far.
That puts the U.S. on pace for close to a 50% increase in murders compared to two years ago, says Aaron Chalfin, a criminologist at the University of Pennsylvania. "It's wiped out maybe 20 years of progress in reducing homicides."
Yes, but: The homicide rate was 7.8 per 100,000 people in 2020, according to the CDC - still well below the peak of 10 homicides per 100,000 in the early 1980s.
And the crime increase of 2020 was almost solely concentrated in homicides and shootings - a report released last month by the moderate Democratic group Third Way found the overall crime rate, including property crimes like burglaries, continued to fall in 2020.
The big picture: There is widespread disagreement among criminologists about the factors behind the 2020 murder surge, not to mention about what caused violent crime to climb in the 1960s and fall in the 1990s.
"The pandemic shut down the operations of the criminal justice system in an important way, from police stopping people to the workings of the courts," says Jen Ludwig, director of the University of Chicago Crime Lab.
Beyond the criminal justice system, the very fabric of community life - everything from schools to businesses to organizations dedicated to curbing violence - was unable to function, leading to what Princeton University criminologist Patrick Sharkey calls a "feeling of people being left on their own in public spaces, creating the conditions for violence."
There's also strong evidence of a pullback of policing following the protests sparked by the murder of George Floyd. In Philadelphia, which this year is on track for a record number of homicides, data gathered by ProPublica indicates that police vehicle and pedestrian stops declined by more than two-thirds from late May to mid-June last year.
As the police pulled back, so did communities. A recent working paper from Desmond Ang at Harvard's Kennedy School of Government found the number of 911 calls made for every gun death or injury fell by nearly half after Floyd's killing on May 25.
What they're saying: "It's all part of a larger legitimacy crisis," says Justin Nix, a criminologist at the University of Nebraska. "The police pull back, citizens feel less inclined to report crimes to the police, and a small subset of the population that is more inclined to criminally offend maybe feels emboldened enough to offend more."
Between the lines: The U.S. had more than one gun per person even before the pandemic, but FBI background checks for firearms spiked as the pandemic took off in March 2020 and set a record for the year as a whole.
Some of those guns end up as the main instruments in violent crime - FBI statistics show 77% of the homicides in 2020 were committed with a gun, up from 74% in 2019 and the highest percentage on record.
But beyond the sheer number of guns is how readily available they were. Police stops in Chicago dropped 85% between January and June 2020, but police were more than twice as likely to recover an illegal gun during those stops.
"There's compelling evidence that gun carrying in public places last year was up, not just buying," says Nix.
What to watch: Violent crime itself can spread like a virus, as one murder leads to others, notes John Roman of the National Opinion Research Center at the University of Chicago.
"There's a lot of trauma, and a lot of desire for retaliation," he says. "Retaliation creates its own cycle, and we're still in the middle of that cycling."