Christie's policy focus isn't lifting him out of the pack

Even if Christie makes the cut, though, the debate stage won't afford him the ability to delve into his policy specifics, said Julian Zelizer, a professor of history and public affairs at Princeton University.

Christie's challenge, Zelizer said, will be to draw broader contrasts with rivals such as former Florida Gov. Jeb Bush, U.S. Sen. Marco Rubio from Florida, and Wisconsin Gov. Scott Walker.

"The burden on him is to say something that grabs people's attention and makes him look different fundamentally than some of these other candidates," he said.