This is President Obama's second trip south of the border in less than four months. When Mr. Obama visited Mexico City in April, one of his aides became sick and returned home.

奥巴马在4月访问墨西哥时，他的一名助理因生病返回美国。

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On Wednesday the system left a rare thin layer of snow across the deserts of Arizona, New Mexico and Southern California -- as far south as the border with Mexico.

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The violence in Mexico and elsewhere south of the border could spill over to the United States, says the report, issued in November by the U.S. Joint Forces Command.

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While he was in office, Bill Clinton launched Operation Gatekeeper to militarize the U.S.-Mexico border south of San Diego and signed legislation to make it easier to deport people and harder for those slated for deportation to contest their removal.

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