FILE - In this April 10, 2000, file photo, a marker embedded in the pavement marks the imaginary line between the United States and Mexico at the San Ysidro border checkpoint between San Diego, Calif., and Tijuana, Mexico. The rare conjunction of two major cities, Tijuana and San Diego, with Los Angeles to the north, make it one of the busiest border crossings on the planet. The U.S. National Guard faces a vastly different environment than it did on its last two deployments to the border with Mexico, with far fewer illegal crossings and more Central Americans than Mexicans coming. (AP Photo/Damian Dovarganes, File)