The Department of Homeland Security has contingency plans to rush additional personnel and other resources, including the U.S. military, to parts of the southern border if law enforcement agencies on the ground are overwhelmed by spillover effects from escalating criminal violence in Mexico, department officials say. The escalation has included videos of torture and executions posted on the Web - a tactic former officials say was likely copied from Muslim terrorists - and hours-long firefights between authorities and criminals toting large-caliber automatic weapons. A State Department travel advisory for U.S. citizens last week compared these incidents to "small-unit combat." The...