Cruz is the quintessential darkhorse IMO. He has a very clear and reasonable path to victory. It largely just depends on if things that have decent probability of happening, happen. Basically his plan has always been to be "the outsider" and christian conservative candidate, which he has done extremely well. The problem is that even bigger outsiders in Trump, Carson, and Fiorina are getting that vote for now. Cruz thinks that their novelty will wear off then those votes will gravitate towards him. This could certainly happen, and given how powerful of a debater and communicator (and fundraiser) he is, he's got everything it would take to have a Reaganesque win. His problem is the establishment hates him, but the establishment may not get their pick this cycle.