Residents cast their vote at the Shoesmith Elementary School near President Barack Obama's house, in southern Chicago, Illinois, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Zhang Jun)

Residents cast their vote at the Shoesmith Elementary School near President Barack Obama's house, in southern Chicago, Illinois, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Zhang Jun)

A man casts his vote at a polling station in Chicago, Illinois, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Wang Chengyun)

A man casts his vote at a polling station in Chicago, Illinois, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Wang Chengyun)

People queue up to vote outside a polling station in Washington D.C., capital of the United States, on Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Wang Yiou)

A resident casts his vote at a polling station in Chicago, Illinois, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Yang Lei)

Voters walk into Chinese Evangelical Free Church in Montery Park, California, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Zhao Hanrong)

A resident fills her ballot at a polling station in Chicago, Illinois, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Yang Lei)

A man registers for vote at Chinese Evangelical Free Church in Montery Park, California, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Zhao Hanrong)

People gather to vote at a makeshift tent, which is used as a polling station in Rockway, New York, the United States. The Rockaway Peninsula was hit by Hurrican Sandy last week. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Wu Jingdan)

A voter has his ballot scanned at a polling station in Manhattan, New York, the United States, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Wu Jingdan)

A voter walks into a polling station for voting in San Francisco, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Liu Yilin)

A voter attends the voting at a makeshift tent, which is used as a polling station in Rockway, New York, the United States. The Rockaway Peninsula was hit by Hurrican Sandy last week. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Wu Jingdan)

A voter scans his ballot at a polling station in San Francisco, Nov. 6, 2012. The quadrennial U.S. presidential elections kicked off Tuesday. Xinhua/Liu Yilin)