Attack likely to exploit existing network of cross-border human, drug traffickers. A nuclear terrorist attack on the U.S. is better than an even bet in the next 10 years, says a former assistant secretary of defense and author of a book on the subject. "Based on current trends, a nuclear terrorist attack on the United States is more likely than not in the decade ahead," says Graham Allison, director of the Belfer Center for Science and International Affairs at Harvard's Kennedy School of Government and author of "Nuclear Terrorism: The Ultimate Preventable Catastrophe." Allison, who has testified before Congress on...