From left, Sen. Jeff Flake, R-Ariz., Sen. Chuck Schumer, D-NY, Sen. John McCain, R-Ariz., and Sen. Michael Bennett, D-Colo, arrive at a news conference after their tour of the Mexico border with the United States on Wednesday in Nogales, Ariz. The senators are part of the "Gang of Eight," a larger group of legislators collaborating on changes to immigration. Ross D. Franklin/AP hide caption

itoggle caption Ross D. Franklin/AP

Democrat Richard Carmona (left) and Republican Rep. Jeff Flake shake hands before Thursday's debate in Chandler, Ariz. Ross Franklin/AP hide caption

itoggle caption Ross Franklin/AP