With the crucial New York primary approaching, Hillary Clinton tried out a new attack against Bernie Sanders's gun record at an event in Port Washington, New York:

[Sanders] frequently says, "We're a small, rural state, we have no gun laws." Here's what I want you to know: Most of the guns that are used in crimes and violence and killings in New York come from out of state. And the state that has the highest per capita number of those guns that end up committing crimes in New York come from Vermont. So this is not, "Oh, I live in a rural state, we don't have any of these problems." This is, you know what, it's easy to cross borders. Criminals, domestic abusers, traffickers, people who are dangerously ill, they cross borders too. And sometimes they do it to get the guns they use.

Some parts of the media have not taken kindly to the attack. At the Democratic debate on Thursday, April 14, moderator Wolf Blitzer questioned if this was really a fair attack. The Washington Post gave Clinton's claim "Three Pinocchios." (The Sanders campaign pointed me to the Washington Post's "fact check" when I asked them about the issue.)

Specifically, journalists have pointed to federal data of guns in New York traced by the Bureau of Alcohol, Tobacco, Firearms, and Explosives. Just 55 of 4,585 guns traced by the agency were from Vermont. A bulk of guns came from the South, particularly Virginia and Georgia. Nearly 1,400 came from New York itself. (The ATF doesn't trace all guns used in crimes — just those that law enforcement agencies request.)

It's true that, as Clinton said, Vermont is overrepresented in this data relative to its very small population. But in total, guns from the state only made up about 1 percent of New York's gun problem — a fairly small impact.

Looking at this data, the Post said Clinton "carefully crafted her talking point to find the particular government data that support her point, which gives a wildly different view than how trafficking flows are tracked. We do not find the per capita measure as a fair assessment of gun flows from Vermont into New York."

But this kind of misses the point of Clinton's claim: The issue is not about how much of an impact Vermont alone has, but how states in general can enable violence beyond their borders with weak gun laws.

What Clinton's attack is really about

Now, Clinton's focus on Vermont is a stretch, even if her Democratic rival is one of its senators. Vermont supplies about 1 percent of New York's guns; even if that's high relative to Vermont's population, it's a tiny fraction of New York's gun problem.

But it's absolutely true that New York's gun restrictions are significantly weakened by other states' loose gun laws. According to ATF data, just 30 percent of traced guns come from New York. The rest come from other states — most prominently, Virginia, Georgia, Pennsylvania, and Florida, all of which have much weaker gun laws than New York. In the past, this gun shipment route from the South to New York has earned the name "the Iron Pipeline."

This isn't just a New York issue or exclusive to the South. Other research has found that the guns used in crimes in Chicago, which has strict gun laws, by and large come from outside the city and state — places such as Indiana or Mississippi that have fairly weak gun laws, or even other parts of Illinois that don't have gun laws as strict as Chicago's.

It isn't even just a domestic problem. Other federal data suggests that most of the guns used in crimes in Mexico, which has strict gun laws, can be traced back to the US, which has generally weak gun laws.

All of this goes to show that state-level gun restrictions can only go so far. As long as there aren't universal, federal laws that stop or slow the flow of guns around the US, criminals are going to be able to simply cross a few borders to stock up on firearms. Clinton was simply articulating that point, using Vermont as a (faulty) example.

Clinton's attack cuts against some of Sanders's rhetoric on guns

Clinton is essentially trying to cut down Sanders's claims that setting a national gun policy is about finding the right balance between "rural" and "urban" cultures, which suggests that different places should have different gun laws.

For example, Sanders said last year on CNN:

The people in my state understand — I think pretty clearly — that guns in Vermont are not the same thing as guns in Chicago or guns in Los Angeles. In our state, guns are used for hunting. In Chicago, they're used by kids in gangs killing other kids, or people shooting at police officers. … We need a sensible debate about gun control which overcomes the cultural divide that exists in this country, and I think I can play an important role in this.

While this may be true, the research shows that having states with different gun policies just because they have different cultures is simply untenable. As long as one state allows very loose access to guns, any other state's attempts to impose serious restrictions on firearms is going to be weak, since people can just go to the state with weaker laws to pick up a firearm.

Yet Sanders has consistently used the rural-urban line of argument to defend his mixed record on guns, including his previous votes against the federal law that established background checks, his vote for a bill that critics said would limit the ATF's ability to take away licenses from law-breaking gun dealers, and his vote for protecting gun manufacturers and sellers from lawsuits. (Sanders has since backed away from some of these votes.)

But the only way to stop one state from allowing the flow of guns to another is federal policy, and that federal policy will likely have to be much stricter than what Vermont and many other states have right now. Sanders's rhetoric seems to miss that point — and Clinton is trying to capitalize on it.