They also cited steps to combat drug cartels in Mexico and reduce the flow of weapons and drugs across the shared border.  "We are very mindful that the battle President Calderon is fighting inside of Mexico is not just his battle, it's also ours," Obama said. "We have to take responsibility just as he's taking responsibility. And that's true with respect to guns flowing from north to south, it's true about cash flowing north to south."  The two presidents discussed "how we can strengthen border security on both sides" to curtail the weapons and drug traffic," Obama said, calling it "a challenging task."  Calderon praised Obama for the joint responsibility on border issues and said, "There's a great deal that has to be improved in terms of how to share information, how to trace the weapons."  He noted the "large restrictions that President Obama and his administration have at a political level" involving conservative opposition to tightening gun laws and immigration reform.  "We all want to have a safe border," Calderon said. "I believe it's possible, although it will require huge technological and financial resources to achieve it," including advanced detection technology that is non-intrusive.  Calderon's Washington's visit came 16 days after American immigration and customs enforcement agent Jaime Zapata was shot and killed on a Mexican provincial highway in the central state of San Luis Potosi. His partner, Victor Avila Jr., was also shot, but survived.  Mexican authorities have arrested Julian Zapata, nicknamed "Tweety," and five other men in connection with the crime. Last weekend they arrested Sergio Mora Cortes, alias "El Toto," the leader of the Zetas cartel cell that operates in San Luis Potosi state.
Mexican President Felipe Calderon and U.S. President Barack Obama on Thursday praised each other for increased cooperation on border security and commerce issues after talks at the White House that