Responsible immigrants who feel vulnerable to begin with have to balance their fear of the gangs with their fear of the authorities. (According to the Pew report, "just over half of all Hispanic adults in the United States worry that they, a family member or a close friend could be deported.") In many cases, says Baca, parents are intimidated by their gang-member children.

To some extent, this is part of a long-familiar pattern. For decades sociologists have observed what's called "the paradox of assimilation": the children and grandchildren of immigrants in the United States absorb the violent ways of U.S. society, and they are more likely than their parents to get involved with criminal activity. That's especially true, of course, if their parents' dreams of a better life are thwarted and the children are cut off from education and jobs.

But in this world of increasingly porous frontiers, what goes on inside the United States is hard to isolate from what happens abroad. The problem with Laredo, Texas, for instance, is not the influx of new immigrants in the 1990s, which, once again, correlated with major declines in Laredo's crime rates throughout the decade. It was the rise of gangs just across the border and the failure of Mexican authorities to crack down on them effectively that led to violence to spill over onto the U.S. side of the Rio Grande.

The most infamous gangs of the moment come from farther away and operate deeper inside the United States. Mara Salvatrucha, or MS-13 as it's called, had its origins in the aftermath of El Salvador's savage civil war and the gang rivalries of the Los Angeles barrios where many Salvadoran refugees fled. Over the last 15 years MS-13 has spread across the United States, often reaching into small towns and suburbs. "MS-13 is far more violent and operates like a crime syndicate," says Baca. "It's ruthless, organized and operating on a scale that is international."

The many mass arrests and deportations of MS-13 members over the last few years have, in fact, created a symbiotic spiral of violence, with the murderous cultures of the United States and El Salvador feeding off each other as gang members move back and forth. Joaquín Villalobos, a former Salvadoran guerrilla leader who now works as an adviser on conflict resolution to several governments, says "the gang culture is North American, while what grew in Central America was a very primitive culture of violence with even fewer scruples. From that mix has emerged the most dangerous gang we know about."

So here's my question: if gangs cause crime, while the vast majority of immigrants help reduce crime, why don't our presidential candidates make gangs—and not immigrants—the issue?

© 2007