There are four tiers of candidates going into the second GOP debate. One candidate who is most likely to get the nomination, two candidates who are serious contenders, four candidates who are long-shots, and those candidates that are negligible.
1) Most likely: Jeb Bush has held onto this spot for all of 2015. His first debate was weak and he has moved down from around 45% to around 35%, but he is still the commanding favorite.
2) Second tier: Donald Trump has joined the second tier by surviving. The longer he lasts on top of the polling the more he will creep up in the probability of victory. Marco Rubio has been a clear contender to Bush for all of 2015 and a strong first debate (combined with Scott Walker’s less commanding performance) has solidified his hold within this slot.
3) Very Unlikely: Ben Carson, John Kasich, Carly Fiorina are all on the upward swing into very unlikely. Kasich and Fiorina are fueled by strong first debates and Carson by strong polling. Walker joins this group on the downswing.
4) Negligible: Ted Cruz, Mike Huckabee, Chris Christie, and Rand Paul.
Sources: Betfair, Hypermind, PredictIt, http://twopointoh.predictwise.com/politics/2016RepNomination
There are two competing crowd sourced data points for the 2016 GOP nomination: polls and prediction markets. Polls provide a snapshot of what the GOP voter would do if the election were today, while prediction markets provide a prediction of what will happen when the GOP voters actually vote in 2016.
Both Trump and Carson do much better in polls than prediction markets, because the markets discount for future success and/or failure, not just current standing. These two outsiders are more likely to stumble in the next few months of campaigning than more vetted and/or tested career politicians. Conversely, Bush is strongly in third place in the polling, making him the most likely benefactor of a late drop by Trump and Carson. If the GOP establishment needs to coalesce around an anti-Trump or Carson, Bush is currently the most likely candidates who can put that together.
Sources: Huffington Post's Pollster, http://twopointoh.predictwise.com/politics/2016RepNomination