Introduced into war-ravaged El Salvador, the gang spread quickly among demobilized soldiers and a younger generation accustomed to violence. Many deportees who had been only loosely affiliated with MS-13 in the U.S. became hard-core members after being stranded in a country they did not know, with only other gang members to rely on. As the gang proliferated and El Salvador tried to crack down on it, some deportees began finding their way back into the U.S.—in many cases bringing other, newly recruited gangsters with them. Deportation, incubation, and return: it’s a cycle we’ve been caught in ever since.

Today, MS-13 has perhaps 6,000 to 10,000 members in the United States. It has grown moderately in recent years and now has a presence in 43 states (up from 32 in 2003 and 15 in 1996). Most members of the gang are foreign-born. Since 2005, ICE has arrested about 2,000 of them; 13 percent have been deported before.

Salvadoran police report that 90 percent of deported gang members return to the U.S. After several spins through the deportation-and-return cycle, MS-13 members now control many of the “coyote” services that bring aliens up from Central America. Deportation—a free trip south—can be quite profitable for those gang members who bring others back with them upon their return.

The surge in arrests and deportations in the past three years coincides with a serious U.S. effort to improve coordination with Central American governments—the better to track gang members wherever they go. But states like El Salvador have a lot to keep track of these days. MS-13 and other gangs born in the United States now have 70,000 to 100,000 members in Central America, concentrated mostly in El Salvador, Honduras, and Guatemala. The murder rate in each of these countries is now higher than that of Colombia, long the murder capital of Latin America.

Meanwhile, the U.S. continues to repeat the mistakes it made in the ’90s. Most ICE arrests have been for immigration-related offenses, not criminal offenses. Suspected “associates” are lumped in with gang members, which only reinforces gang ties; with dabblers and minor offenders, experts agree that anti-gang intervention programs are better at preventing gangs’ growth. For hard-core gang members, quickie deportations on immigration charges are often no more than short-term fixes; lengthy American prison sentences would be more effective.

Only the U.S. has the law-enforcement personnel, the criminal-justice system, and the money to deal with the problem. Although the idea is poison in the current political climate, the way to get rid of these gangs, paradoxically, may involve keeping them here.