There are episodes of school violence every day in America, but few are as terrifying as the one that didn't quite come off at Winslow Township High School in New Jersey a couple of months ago.

Four teens hatched a plot to bring guns to school and kill dozens of teachers and students whose names were on a hit list. Two female students came to school officials with rumors of what was being planned, and police caught the plotters. In the end, no one was harmed.

The narrowly averted tragedy shook the school and nearby Camden, New Jersey, where gun violence is epidemic. Camden's murder rate, 10 times the national average, has made it the nation's most dangerous city two years in a row. But local officials have also repeatedly pointed out that, on their own, they couldn't solve the problem of gun violence. "We can't arrest our way out of this," one police officer said.

Camden Mayor Gwendolyn Faison elaborated: "We don't manufacture the drugs, we don't make the guns, but we must deal with the effects of each. We cannot deal with these issues by ourselves."

It's fair to say that most U.S. mayors feel the way Faison does. They may boast about declining crime rates, but they know full well that their communities have a gun problem. And yet they aren't optimistic about making progress without strong action by the federal government. In April, 15 of the nation's big-city mayors met in a New York City summit to say that the feds had to act. "It is time for national leadership in the war on gun violence," said New York Mayor Michael R. Bloomberg.

The summit failed to nudge Congress or state officials, but it did highlight the dilemma of gun violence. Mayors get the phone calls about the shootings. Their citizens look to them for action. But they've found how hard it is to take the guns off the street in the absence of some additional authority.

Gun manufacturers counter that mayors ought to focus on enforcing existing laws, rather than pleading for new ones. If the laws were tougher, the industry says, gun traffickers would simply ignore them, ordinary citizens would lose their rights and gun violence would be unchanged.

Local officials generally don't accept that. In their view, it's unrealistic to think they can stem gun violence as long as gun traffickers can buy large supplies of handguns in states with lax rules (such as Pennsylvania) and peddle them in tough gun-control states (such as California and New York). One study found that 94 percent of all guns used in New York City crimes were purchased elsewhere.

Four states--California, Maryland, South Carolina and Virginia--have enacted a "one gun a month" plan to limit how often individuals can purchase weapons. However, in other states, where hunting is a near- religion, even that modest step is politically unlikely. In Wisconsin, hunters only half jokingly call the start of deer season "holy week." That makes it tough for legislators to act.

There is little evidence that crime goes down in states that enact a "one gun a month" limit. It's possible that adjoining states do benefit somewhat from a reduced flow of firearms across the border. But most legislators would prefer to see the stricter laws in neighboring jurisdictions so they can avoid the political pitfalls of cracking down on their own citizens.

Some gun-control advocates continue to argue that the best way to deal with the issue is to redefine it: away from gun control and toward local control. In other words, if local officials really had the authority to take on gun violence by any means they saw fit, experiments would flourish and the entire country would find out what worked.

But aside from the inevitable constitutional questions about such an approach, the depressing likelihood is that no policy restricted to the local level would work. Gun violence is a national problem that demands a federal solution--or, at least, tough state laws to cut down the gun trafficking. State and federal officials say they don't have good evidence about what really works, and that makes it harder for them to make politically tough decisions. But unless they do, we may be listening to the same arguments in 2016 that we're listening to in 2006.