In the GOP race, you have the "primary within a primary" to see who will become the anti-Jeb (aka "conservative alternative").
The way this is is supposed to work, is that the anti-Jeb is actually a ringer, controlled opposition, who lays down and gives it to Jeb.
Rand puts a wrinkle in the plan (as Ron did before), since he's not an establishment ringer.
So two possibilities:
(1) Rand becomes the anti-Jeb and there's a real contest, which he may or may not win,
or (2) someone else becomes the anti-Jeb, which guarantees that Jeb will be the nominee.
Rand's odds of becoming the anti-Jeb? The real contenders for the slot, I'd say, are Rand, Walker, & Rubio. Let's give them each at equal chance, so Rand's chance is 33%. Then, supposing Rand does become the anti-Jeb, I'd give him a 50% chance against Bush. Doing the math, Rand has a total chance at the nomination of 16.5%. Since Walker and Rubio would each, as anti-Jeb, definitely lose to Bush, they have a 0% chance at the nomination. So, Rand 16.5%, Bush 83.5%.
...that's how I see it at the moment, anyway.
...and, of course, Hillary will be the Dem nominee (and the next POTUS unless Rand gets the nomination).