ABC News' Christine Byun reports: Republican presidential candidate former Sen. Fred Thompson, R-Tenn., fleshed out his position on immigration reform while campaigning at a townhall meeting in Sioux City, Iowa Friday. His loudest and most frequent applause came during a lengthy response to a question regarding the status of illegal immigrants living in the United States. "If we catch illegal immigrants who are here, they need to be deported," Thompson said. "If they want to get back in the right way, get in line with everybody else." He also called upon Mexico President Felipe Calderon to focus on building his...