In Nogales, Arizona on the dusty hilltops west of U.S. Interstate 19, National Guardsmen with M-4 rifles peer down from camouflage tents and surveillance posts, so close to the border fence they can almost watch TV through the windows of Mexican homes on the other side.
The troops are members of the Arizona National Guard and Arizona Air National Guard, sent by the Obama administration last summer amid heightened concerns about lawlessness and spillover drug violence along the border. Of the 1,200 Guardsmen deployed to the U.S.-Mexico divide, 560 are here in Arizona, where lawmakers pushed hard for a larger military deployment during a statewide crackdown on illegal immigration last year.
"We are extra eyes and ears," said Brig. Gen. Jose Salinas of the Arizona National Guard. "We're out in the open, trying to act as a deterrent, ready to respond to any kind of weird incident out there."
Salinas said the one-year National Guard mission is a stopgap measure to give U.S. Customs and Border Protection time to hire more agents. But worsening cartel violence in Mexico and several high-profile killings on the U.S. side have raised calls for more National Guardsmen along the border, even though illegal immigration and crime in the region have declined.
Border-state legislators from both parties - particularly following the Dec. 14 killing of a Border Patrol agent just north of Nogales - say they view the U.S. military presence as a long-term necessity, despite rules that mostly limit the Guardsmen to watching the fence line and prevent them from making arrests or seizing drugs.
"The border with Mexico is our third front, after Afghanistan and Iraq," said Rep. Ted Poe (R-Tex.), who has proposed legislation allowing border-state governors to send 10,000 Guardsmen to the area. "Whether you want to call it a war zone, or whatever, we need the National Guard because of criminal violence along the border."
Human rights organizations and policy analysts say the U.S. military deployment endangers civilians and is wasteful, pointing to FBI statistics showing that crime in many areas on the U.S. side is at its lowest point in years.
Drug violence has killed more than 30,000 in Mexico in the past four years, and the country's powerful trafficking gangs have turned Mexican towns along the U.S. border into bloody urban battlefields.
Rep. Gabrielle Giffords (D-Ariz.), whose district includes the state's southeast corner, where 58-year-old rancher Robert Krentz and his dog were shot and killed in March, said the troops help keep the mayhem on the other side.
"Mexican and American authorities have gone after cartel kingpins, and because of the disruption, these gangs are going after each other," Giffords said. "We're seeing tremendous violence along the border that we haven't seen in the past."
Once overwhelmed and understaffed, U.S. Customs and Border Protection has been on a hiring binge in recent years, increasing its number of agents from 10,000 in 2004 to more than 20,500 today, Department of Homeland Security figures show. Meanwhile, the number of suspected illegal immigrants apprehended by the Border Patrol has plunged more than 60 percent, from an all-time high of 1.1 million in fiscal 2004 to fewer than 447,500 last fiscal year.
High unemployment in the United States is a major reason for the decrease, experts say. Although fewer illegal migrants are crossing and several large urban areas have become safer, drug seizures have increased and tougher enforcement is pushing traffickers into more remote rural areas. That has led to several high-profile killings that have fueled fears of encroaching violence.
The most recent came Dec. 14, when Border Patrol Agent Brian Terry was killed in a shootout with a group of bandits devoted to robbing drug smugglers and immigrants. Four suspects were arrested in the killing, and a fif