GOP presidential candidates attend debate in Des Moines, Iowa

2016 Republican presidential candidate Florida Sen. Marco Rubio responds to a question during a GOP debate hosted by Fox News, January 28, 2016, in Des Moines, Iowa. Billionaire businessman Donald J. Trump has boycotted the debate, which is the final one before Iowa's first-in-the-nation caucuses, February 1. Photo by Mike Theiler/UPI