The Republican presidential candidates in Wednesday's debate take the stage at the Ronald Reagan Presidential Library and Museum in Simi Valley, Calif.

With Jeb Bush between them, Donald Trump and Scott Walker square off during Wednesday night's debate.

Donald Trump speaks as Jeb Bush listens Wednesday night at the Ronald Reagan Presidential Library and Museum.

Donald Trump looks on as Ben Carson speaks during Wednesday night's debate.

Chris Christie responds to a question as CNN's questioners Dana Bash, center, and Hugh Hewitt listen during Wednesday night's Republican presidential debate.

Positioned between his rivals Ben Carson, left, and Jeb Bush, Donald Trump, speaks as during the CNN Republican presidential debate in Simi Valley, Calif.

Sen. Ted Cruz of Texas makes a point during the debate.

Carly Fiorina speaks as Wisconsin Gov. Scott Walker listens.

Sen. Rand Paul of Kentucky speaks during Wednesday night's debate.

Chris Christie, right, speaks as John Kasich looks on.

Former Arkansas Gov. Mike Huckabee speaks as Sen. Marco Rubio of Florida looks on during the debate.

Donald Trump and Jeb Bush slap hands near the end of the debate, after Bush said his Secret Service code name as president would be “Eveready.” Bush said to Trump that it's a “high-energy” name – noting Trump’s criticism of Bush as a low-energy candidate.

Republican presidential candidates Rick Santorum, left, George Pataki, second from left, Bobby Jindal, second from right, and Lindsey Graham talk at the finish of their debate Wednesday night. The Associated Press