Standoff over troops at U.S.-Mexico border

Brian de Vallance, senior counselor to Napolitano, said she "feels we have an obligation to do whatever we can do to disrupt those forces that are destroying lives in over 200 American cities. ... It comes down to whether folks want to be as aggressive as we can be against the cartels and take every advantage of this historic opportunity" of cooperation between Mexico and the United States.

The debate goes to the heart of the military's role, which has expanded since the 2001 terrorist attacks, with an increasing commitment of troops and resources to homeland defense, particularly to help state and local officials respond to a nuclear attack or other domestic catastrophe. The deployment of new troops to the border would represent a mission the military has not traditionally embraced.

"What we're seeing is here is a move toward reframing where defense begins and ends," said Bert B. Tussing, director of homeland defense and security issues at the U.S. Army War College's Center for Strategic Leadership. "Traditionally the military looks outward, but looking outward has begun a lot closer to home, and it may involve looking just across the border."

Texas Gov. Rick Perry (R) requested 1,000 Guard troops in January that he later said could form 24 border reconnaissance platoons, support Texas Ranger and parks and wildlife tracking teams, and back up air and marine operations. Perry, Arizona Gov. Jan Brewer (R), California Gov. Arnold Schwarzenegger (R) and New Mexico Gov. Bill Richardson (D) subsequently asked Congress to add personnel to the National Guard's Counter-Drug Program in their states. Currently, troops provide translators, reconnaissance and administrative support, relaying aircraft surveillance images, for example.

Border states bear "unique and/or disproportionate" costs of dealing with illegal immigration, drugs and violence, Brewer wrote.

"It is abundantly clear that additional resources are needed — and needed now," the governors wrote in a separate letter.

The fight is largely over money. For the past two years, Pentagon budget officials have tried to slash funding for state drug-fighting operations, citing the financial strain of waging wars in Iraq and Afghanistan. And military officials say governors could pay for their own guard units.

But governors contend that securing the border is a federal responsibility and that Washington should cover the cost.

Paul McHale, Gates's assistant secretary for homeland defense until early this year, said the broader worry is strategic. "The real concern is, if it works once, and it works a second time ... at some point a temporary mission becomes permanent," he said. "Do it four or five times over a decade, and the political and military repercussions are likely negative."