Republican presidential candidates participate in two separate debates, one after the other. The “undercard” debate features candidates who are low in the polls: Sen. Lindsey Graham, Gov. Bobby Jindal, Gov. George Pataki and Sen. Rick Santorum. The main debate, broadcast in prime time, features the top 11 candidates in the polls: Gov. Jeb Bush, Dr. Benjamin Carson Jr., Gov. Chris Christie, Sen. Ted Cruz, Carly Fiorina, Gov. Mike Huckabee, Gov. John Kasich, Sen. Rand Paul, Sen. Marco Rubio, Donald Trump and Gov. Scott Walker.