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Women and children wait in a holding cell at a U.S. Border Patrol processing center after being detained by agents near the U.S.-Mexico border on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455037698 )

Formula for toddlers awaits new arrivals to a U.S. Border Patrol processing center for immigrants detained near the U.S.-Mexico border on September 8, 2014 in McAllen, Texas. (Photo by John Moore/Getty Images) ( 455037704 )

Junvenile immigrants wait in a holding cell at a U.S. Border Patrol processing center for immigrants detained near the U.S.-Mexico border on September 8, 2014 in McAllen, Texas. The sign, written by the U.S. Centers for Disease Control (CDC), reads "Maintain Calm and Wash Your Hands." (Photo by John Moore/Getty Images) ( 455037702 )

Women and children sit in a holding cell at a U.S. Border Patrol processing center after being detained by agents near the U.S.-Mexico border on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455037686 )

Families of Central American immigrants turn themselves in to U.S. Border Patrol agents after crossing the Rio Grande River from Mexico on September 8, 2014 to McAllen, Texas. Although the numbers of such immigrant families and unaccompanied minors have decreased from a springtime high, thousands continue to cross in the border illegally into the United States. The Rio Grande Valley sector is the busiest area for illegal border crossings, especially for Central Americans, into the U.S. (Photo by John Moore/Getty Images) ( 455034412 )

Families of Central American immigrants turn themselves in to U.S. Border Patrol agents after crossing the Rio Grande River from Mexico on September 8, 2014 to McAllen, Texas. (Photo by John Moore/Getty Images) ( 455034428 )

Families of Central American immigrants turn themselves in to U.S. Border Patrol agents after crossing the Rio Grande River from Mexico on September 8, 2014 to McAllen, Texas.(Photo by John Moore/Getty Images) ( 455034406 )

A U.S. Border Patrol agent looks towards Mexico from the bank of the Rio Grande River on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455034400 )

A footprint, probably of an immigrant smuggler, according to a Border Patrol agent, lies near bank of the Rio Grande River at the U.S.-Mexico border on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455034396 )

Texas National Guard troops watch for illegal immigrant crossings as a full moon rises near the Rio Grande River at the U.S.-Mexico border on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455034392 )

Texas National Guard troops watch for illegal immigrant crossings near the Rio Grande River at the U.S.-Mexico border on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455034418 )

U.S. Border Patrol agents detain an undocumented immigrant along a railroad track near the Rio Grande River at the U.S.-Mexico border on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455034444 )

MISSION, TX - SEPTEMBER 08: Families of Central American immigrants, including Lorena Arriaga, 27, and her son Jason Ramirez, 7, from El Salvador, turn themselves in to U.S. Border Patrol agents after crossing the Rio Grande River from Mexico on September 8, 2014 to Mission, Texas. (Photo by John Moore/Getty Images) ( 81563975 )

MISSION, TX - SEPTEMBER 08: Families of Central American immigrants, including Jamie Gonzales, 26, and her son Jose Manuel, 4, from El Salvador, turn themselves in to U.S. Border Patrol agents after crossing the Rio Grande River from Mexico on September 8, 2014 to Mission, Texas. (Photo by John Moore/Getty Images) ( 81563911 )

A U.S. Border Patrol agent prepares a report after he and colleagues detained an undocumented immigrant near the Rio Grande River at the U.S.-Mexico border on September 8, 2014 near McAllen, Texas. (Photo by John Moore/Getty Images) ( 455034398 )

MISSION, TX - SEPTEMBER 08: Families of Central American immigrants turn themselves in to U.S. Border Patrol agents after crossing the Rio Grande River from Mexico on September 8, 2014 in Mission, Texas. (Photo by John Moore/Getty Images) ( 81563754 )