CALEXICO, CA - OCTOBER 9:  Customs and Border Protection agent Barbara Mandel shines a flashlight on a fresh track that was discovered while on patrol in Calexico, California October 9, 2007. Immigration continues to be a hot topic among political contenders and economic watchdogs. Getty Images logo Getty Images 25 months ago

CALEXICO, CA - OCTOBER 9: Customs and Border Protection agent Barbara Mandel shines a flashlight on a fresh track that was discovered while on patrol in Calexico, California October 9, 2007. Immigration continues to be a hot topic among political contenders and economic watchdogs.