The four lowest polling Republican U.S. presidential candidates, (L-R) New York Governor George Pataki, former U.S. Senator Rick Santorum, Louisiana Governor Bobby Jindal and U.S. Senator Lindsey Graham, gather onstage in front of former President Ronald Reagan's Air Force One jet for a debate held before the second official Republican presidential candidates debate of the 2016 U.S. presidential campaign at the Ronald Reagan Presidential Library in Simi Valley, California, United States, September 16, 2015. REUTERS/Lucy Nicholson