Ben Carson's former presidential campaign manager Barry Bennett said it's hard to envision a scenario in which Donald Trump does not become the nominee of the Republican Party in 2016.

"By the middle of March, this thing could be well over. At this point, it's getting harder and harder to see how Donald Trump isn't our nominee," Bennett told CNN. "I'm a realist and I believe in data, I believe in polls, and I have not seen a plan out there that is going to take down Donald Trump quite yet."

Asked whether he still believed Carson was the best candidate for president, Bennett would only say that Carson "has the best head and the best heart."

Bennett said the existence of a "shadow campaign" within Carson's team had spoiled his meteoric rise to the top of the polls, but the former campaign manager said he remained proud of what the retired neurosurgeon's formal campaign had accomplished.

"He went from unheard of to number one," Bennett said. "We raised $54 million, 1.1 million donations, largest social media following, but in the end people have decided to go with loud and so we've got to get used to this new reality."