Ben Carson has ZERO chance of winning the Republican nomination.
Presidential primaries (and Presidential elections) are ALL about money and organization, with money being the primary factor.
Ben Carson is a political neophyte who doesn't really seem to care about the "nuts and bolts" of politics. He has had three key staff members quit his campaign, which tells me these three realize he has no chance of winning.
Raising money is paramount to a Presidential bid, and money needs to be raised continuously throughout. Carson will never be able to raise the kind of money he needs to compete against financial heavyweights like Bush (and perhaps Rubio).
Carson may not even be involved in the Republican debates.