Ten Democratic presidential candidates gathered today in Las Vegas, under the auspices of Giffords and March for Our Lives, to talk for a half-hour each at the "2020 Gun Safety Forum." They were questioned individually and sequentially by MSNBC anchor Craig Melvin and audience members; most, if not all of them, connected to some anti-gun-violence group.

Collectively, the first five candidates—South Bend, Indiana, Mayor Pete Buttigieg, former HUD Secretary Julian Castro, Sen. Cory Booker (N.J.), Sen. Elizabeth Warren (Mass.), and former Vice President Joe Biden—supported a set of initiatives they insist have mass popular support, including from gun owners. They argued that these "common sense gun safety" proposals are stymied by a combination of President Trump (who, they stated or implied, must be unseated before anything "sensible" can happen regarding new restrictions on gun owners) and a Congress in the thrall of the gun industry and the National Rifle Association (NRA), with the latter merely standing for the former, not for civil rights or the interests of their gun-owning members.

Audience questions often steered them toward the question of the disproportionate impact of gun violence on black and brown urban communities. (While the candidates didn't run with it, David Hogg, the student activist who was present at the Marjory Stoneman Douglas High School shooting in 2018, linked the issue of gun ownership with "white supremacy" without explanation.) None of the candidates mentioned or alluded to the idea that the illegal drug trade plays a large role in that violence, and that liberalizing federal drug laws might help stem gun violence. Biden, in a complete gun law proposal issued today, does mention specific targeted interventions in affected communities, an idea that National Review's Robert VerBruggen praises due to "good evidence showing that they work, and they focus on specific individuals at severe risk of committing gun violence—not everyday people who own guns legally."

Warren was the only candidate savvy and wonky enough to point out something that analysts from the gun-rights side often point out: that the colorful public tragedies that fuel the political demand for action on gun rights would in most cases not have been affected by most of the proposed "common sense" policies that would merely complicate the lives and actions of the overwhelming number of innocent gun owners.

Still, she thinks, that's not a reason not to impose all of them. She suggested that a slow application of every idea to make gun ownership harder or more onerous, like the constellation of safety features the federal government has mandated for cars over the decades, will add up to the results she seeks. In general, she thinks anything that makes sure there are fewer people possessing fewer guns will be good for America.

While agreeing on the broad strokes, including a need for more mental health resources to curb both suicides and potential homicides, each candidate had their own particular points to make.

Buttigieg stressed his desire to spend a billion dollars to have the Department of Homeland Security keep a watchful eye on domestic speech looking for dangerous hateful extremists as a tool to curb gun violence.

Julian Castro stressed higher excise taxes on ammunition and guns and proposed spending the $600-700 million those taxes might raise on gun violence prevention programs. He also thinks making ammunition more uniquely marked and traceable to the gun or buyer would help law enforcement investigate gun crimes.

Cory Booker stressed that we need federal licensing of gun owners because localities with strict gun laws and high gun violence are importing guns from other places. He repeated his unsupported claim that a Connecticut law requiring a permit to buy a gun cut gun homicides 40 percent.

They all think a federal mandate for universal background checks for all gun purchases—not just those from licensed gun dealers, as is the law currently—should be politically easy.

One point of contention was the political feasibility of a mandatory buyback of "assault weapons," such as the one proposed famously by former Texas congressman and fellow presidential hopeful Beto O'Rourke. (None of them mentioned the vanishingly small number of gun murders, around 2 percent, performed with any kind of rifle, or the criminological consensus that the last ban on new sales of such guns had no appreciable effect on public safety.)

Buttigieg considered mandatory assault weapon buybacks a longshot that would sap political capital from efforts to implement more attainable policies like universal background checks, federal licensing, and "red flag" laws to get guns out of the hands of people believed by their family or associates to be dangerous.

Castro is happy to push for a voluntary buyback, plus registering such weapons so the government knows who has them. But he didn't get fully behind the mandatory angle proposed by O'Rourke. The experiences of New Zealand and other places suggest that getting rid of existing legally owned weapons voluntarily, short of going door-to-door, will be tough.

Booker does want a mandatory buyback but insisted that no law making an existing legally owned weapon illegal would ever lead to government men with guns coming door to door, though, in fact, that's exactly what it led to in California. Booker also insisted on federal "safe storage" laws in response to a woman whose son was accidentally shot with a gun a friend's father had left unlocked-up and loaded.

Warren also said something that should be food for thought for those who insist "gun safety" must be a huge federal political priority: She wants more studies trying to drill down into what causes gun violence and what might reduce it. The existing body of such work does not give much reason to hope that there are easily discoverable social science conclusions that can reasonably guide public action.

It is true that our gun murder rate in the past few years has been rising alarmingly, with uncertain causes, though not yet back to the highs of the 1970s-to-mid-1990s. But over the course of a couple of decades from the early '90s to the early '10s, we saw our firearms homicide rate fall nearly by half.

It did so without any of these proposed actions from these candidates having any bearing on the outcome, during a period when the number of guns available to Americans and the states where they had the legal right to carry their weapons outside their home both zoomed up, not down. Thus, the connection between all these proposals and lowering gun homicide rates is far from clear.