One of the more memorable aspects of former President Barack Obama's time in office (which feel conspicuously absent under his successor) were his speeches after mass shootings, speeches that became a bit of a morbid ritual, given how regularly the shootings occur. Over time, they grew angrier, more emotional, and more disgusted at America's gun violence problem and Congress's unwillingness to do literally anything to stop it.

"This massacre is therefore a further reminder of how easy it is for someone to get their hands on a weapon that lets them shoot people in a school, or in a house of worship, or a movie theater, or in a nightclub," Obama declared after the Pulse shooting in Orlando, the 133rd mass shooting of 2016. "And we have to decide if that’s the kind of country we want to be. And to actively do nothing is a decision as well."

But let's be clear about precisely what kind of decision is letting events like this recur, most recently in Dayton and El Paso. Congress's decision not to pass background checks is not what's keeping the US from European gun violence levels. The expiration of the assault weapons ban is not behind the gap. What's behind the gap, plenty of research indicates, is that Americans have more guns. The statistics are mind-blowing: America has 4.4 percent of the world's population but almost half of its civilian-owned guns.

Realistically, a gun control plan that has any hope of getting us down to European levels of violence is going to mean taking a huge number of guns away from a huge number of gun owners.

Other countries have done exactly that. Australia, for example, enacted a mandatory gun buyback that achieved that goal, and saw firearm suicides fall as a result. But the reforms those countries enacted are far more dramatic than anything US politicians are calling for — and even they wouldn't get us to where many other developed countries are.

Think about it this way. In 2013, the US had 106.4 gun deaths per million people. That same year, the UK endured 144 gun deaths total — or 2.2 gun deaths per million people.

To get to UK levels, we'd need to reduce gun deaths by over 98 percent. Even if we wanted to reach the same levels as Switzerland — the country with the third-highest rate of gun deaths in the OECD grouping of developed nations, after Mexico and the US — we'd need to drop from 106.4 deaths per million to 30.1, more than a 71 percent reduction.

And here's the truth: Even the most ardent gun control advocates aren't pushing measures that could close the gap. Not even close.

What happened in Australia

Plenty of research has found a strong correlation between the amount of guns in an area and its gun homicide rate. Countries with more guns have more gun homicides. States with more guns have more gun homicides. Individuals with guns in the house are likelier to be killed or to kill themselves with guns.

So Australia's 1996 gun control was based on a simple idea: They took away a bunch of guns.

After a 28-year-old man killed 35 people at the Port Arthur historic prison colony in Tasmania, Australia, a popular tourist destination, Prime Minister John Howard and his right-wing Liberal Party banned the importation of all semiautomatic and automatic rifles and shotguns, instituted a mandatory national buyback program for such guns, and convinced state governments to ban the weapons outright. In total, about 650,000 weapons — 20 percent of the country's total arsenal by some estimates — were seized and destroyed.

Evaluations after the reforms suggest that they saved lives. A study by Andrew Leigh of Australian National University and Christine Neill of Wilfrid Laurier University estimated that buying back 3,500 guns per 100,000 people led to a statistically significant drop in firearm suicides — 74 percent, in fact, with no parallel increase in non-firearm suicides. While gun control opponents have tried to rebut those results, those responses have been riddled with methodological flaws, and even some of the study's critics have conceded that the laws likely cut down on suicides.

The results on homicides were a little less clear. Leigh and Neill found that the buyback resulted in a 35 to 50 percent decline in the gun homicide rate, but because of the low number of homicides in Australia normally, this change wasn't statistically significant. Supporters of Australia's policy often argue that no mass shootings have occurred since, which is only true for a certain restrictive definition, as in 2014 a man shot himself, his wife, and their three children in a murder-suicide in rural New South Wales.

There have also been a number of non-gun massacres in the years since the Port Arthur massacre. Also in 2014, a mother in a suburb of Cairns, Queensland, allegedly stabbed to death seven of her own children and one niece. In 2000, a man burned a backpackers' hostel to the ground in Childers, Queensland, killing 15.

But the homicide and mass shooting results are almost beside the point. Nearly two-thirds of gun deaths in the US are suicides. If we can reduce them by 74 percent, we'd be saving more than 15,000 lives every year. That doesn't get us to where most developed countries are, but it gets us somewhere near the ballpark of Switzerland.

Why Australia's laws couldn't be adopted in the US (hint: it's not because of the Constitution)

So could it happen in the US? The legal scholars I talked to suggested that an Australia-style program would probably pass muster. If we went further than Australia and also banned handguns, that might cause problems; the Supreme Court struck down Washington, DC's handgun ban in 2008. But Australia's actual system is probably constitutional.

"Courts have consistently upheld bans on military-style semiautomatic rifles because other firearms are equally useful for self-defense," Adam Winkler, a law professor at UCLA and author of Gunfight: The Battle Over the Right to Bear Arms in America, says. "Gun control isn't stalled because of the Second Amendment. It's stalled because elected officials won't pass effective new laws to reduce gun violence."

Sanford Levinson, a law professor at the University of Texas Austin and author of the landmark article "The Embarrassing Second Amendment," concurs: "If such an extraordinary law actually got through Congress (meaning with necessary Republican support), then I find it impossible to imagine that there would be five votes on the Court to say no," he says. "But the real problem, of course, is that there’s not a snowball’s chance in hell of Congress actually passing any meaningful legislation re guns, let alone this kind of quite radical legislation."

And there's the rub. Former President Obama occasionally cited Australia in discussions about gun control, but proposals he and congressional Democrats put forward stopped far, far short of what Australia's done. Obama's plan to tackle gun violence focused on universal background checks for gun sales, banning assault weapons again, and increasing criminal penalties for illicit gun traffickers. That's nowhere near as dramatic as taking 20 percent of America's guns off the street.

Australia provides strong evidence that a form of gun control can save lives. But it's a form of gun control that's too dramatic for most mainstream American politicians to embrace.

Mild measures can do something — but not as much

Milder, easier-to-pass changes would probably also save lives. But the effect sizes are, unsurprisingly, smaller, and vary considerably depending on the study you're looking at.

For example, researchers have found that:

There are a few promising items there, especially when it comes to gun licensing. But taken together, this doesn't look like an agenda that can get the US to European rates of gun deaths.

If you go by the Connecticut experience, licensing can nearly halve gun homicides — but that's by far the most promising finding. Missouri's experience suggests a much smaller effect. And the effects of various interventions aren't additive. An assault weapons ban implemented without universal background checks is going to be more effective than one implemented alongside them, because some of the violence you're trying to prevent would've been foiled by either policy alone.

I asked David Hemenway, a professor at Harvard's public health school who has co-authored dozens of papers on the effects of guns and gun regulation on mortality, if he thought these kinds of smaller-bore reforms could have a big enough effect to bring the US down to European levels. "It's all speculation," he replied. "I suspect it would take a while (decades) for the US to get down to gun violence levels of other developed countries because a) we have so many guns which are durable, and b) we have a gun culture — we tend to use guns more often in more situations than citizens of other developed countries."

It might be easier if there are positive feedback loops, he says — "if the rival gang doesn't have guns, our gang has less need of guns" — but it'll be an uphill battle.

Worse, even these milder-than-Australia policies are considerably more ambitious than legislation with a chance of passing Congress. The Manchin-Toomey bill, the only post-Newtown gun legislation to even come close to becoming law, didn't even establish universal background checks, let alone mandate individual licensing, as Connecticut's law does.

"Even getting half or a quarter of the way down to other nations would save a lot of lives," Hemenway emphasizes. That's undoubtedly true. Background checks, licensing requirements, and the like are positive steps. They save lives, and states should pass them. But America will still be a gun violence outlier, even with them.

This problem is going to be really, really hard to solve

Research on guns is murky. It's necessarily an area where it's hard to do rigorous experimental research, so most studies are conducted after the fact, raising all kind of methodological challenges. That means it's good to be skeptical of big claims from single studies — e.g., that licensing and background checks alone could cut gun homicides by 40 percent.

But we have accumulated some general knowledge all the same. Perhaps the single most supported contention in all of gun research is that more guns mean more gun deaths. The US doesn't just have a gun violence problem because of its lax gun regulation. It has a problem because it has a culture that encourages large-scale gun possession, and other countries do not. That, combined with Australia's experience, makes large-scale confiscation look like easily the most promising approach for bringing US gun homicides down to European rates.

Large-scale confiscation is not going to happen. That's no reason to stop advocating it. (I also want to repeal all immigration laws and give everyone a monthly check from the government with no strings attached, and will argue for those ideas even though they're not politically viable.) But it does mean that we should be realistic about what gun control with an actual shot of passage can achieve. It can make us safer. It cannot make us Europe.

Unless something dramatic changes, gun violence will remain a distinctly American problem for the rest of our lives — background checks or no.

Watch: America's gun problem, explained in 90 seconds