The National Guard stalemate has festered for nearly a year, and frustrated lawmakers are demanding action to stem the spread of violence and drug trafficking that has spilled across the border into their states.
The inaction raises questions about whether the White House is convinced the federally funded deployment is necessary, or whether border states will be forced to bear the costs of dispatching the National Guard troops on their own.
Speaking at the White House on Wednesday with Mexican President Felipe Calderon, Obama said the against the drug cartels.
"As your partner, we'll give you the support you need to prevail," he said, adding that through increased law enforcement on the U.S. side of the border, "we're putting unprecedented pressure on those who traffic in drugs, guns and people."
Fueling the discord over sending the National Guard to the border was the U.S. response to the Gulf oil spill, which has included federal authorization for deploying up to 17,000 National Guard troops.
Those costs, however, are likely to be borne by oil giant BP PLC, which leased the offshore drilling rig Deepwater Horizon that exploded off the Louisiana coast April 20, killing 11 and releasing a huge, continuing oil spill.
The oil spill notwithstanding, border state lawmakers say they need help too.
"If you'll indulge me, we think we have another crisis on the border," Sen. John McCain told Homeland Security Secretary Janet Napolitano at a hearing this week. "I want to know about whether you're going to send the Guard to the border or not."
When she tried to explain other Homeland Security improvements along the border, the senator from Arizona cut her off.
"People's homes are being violated, and their families can't take kids to the bus stop," McCain fumed. "And you are very familiar with the issue, because you yourself asked for the Guard to go to the border back in 2006."
Napolitano, a former Arizona governor, responded that the request involves the White House as well as the Pentagon and the Homeland Security Department, and is still in the interagency process. While she said she would like the decision to be made as soon as possible, she added she could not say when she would have an answer.
"We don't have a resolution on that yet," Air Force Gen. Gene Renuart said in an interview with The Associated Press. Renuart, who headed the U.S. Northern Command until his retirement Wednesday after 39 years of service, added that while money is a point of contention, the greater disagreement centers on what missions the National Guard would perform.
He said the discussion between the Defense and Homeland Security departments continues, and some of the requests "have evolved a bit in this interim period." He did not provide details.
First floated last June, the idea was to use 1,500 National Guard troops temporarily to supplement border patrol agents. The Pentagon and Homeland Security drafted a $225 million plan, but disagreed over who would pay for it and how the troops would be utilized.
Pentagon officials, worried about perceptions that the U.S. was militarizing the border, argued that the National Guard could only be used for particular duties. Military leaders said they did not want National Guard troops to screen vehicles at border points or perform any law enforcement duties, and said the program should be temporary and not tied to any existing program that could get extended.
Defense officials have said that possible missions for the National Guard soldiers could include surveillance along the border, intelligence analysis, helicopter transportation support and aviation surveillance, which likely would involve unmanned aircraft.
In a letter to Obama this week, McCain and Sen. Jon Kyl, also an Arizona Republican, said sending at least 6,000 National Guard to the border - with half focused on the Arizona portion - would immediately improve the safety of Americans there.
White House spokesman Nick Shapiro said the administration has taken a number of steps to improve security at the border, including adding more law enforcement personnel and prosecutors, and increasing cooperation with the Mexican government.
"The president is firmly committed to ensuring that our Southwest border is secure," Shapiro said. "The administration continues to evaluate additional law enforcement options as well as the use of the National Guard, as needed, along the Southwest border."