I did some research. In 2014, the Republican party changed the rules for how they elect Presidential candidates.
First, they changed how state's delegates are portioned out. If a state's primary is held on or before March 14th, the votes are proportional. If a state's primary is held on or after March 15th, the contest is "winner take all", as the majority runner gets all the votes.
Certain states were switched around, as a result of the rule change. Ohio and Florida, which usually play a big role in the general election, were delayed to the "winner take all" time period. Texas, North Carolina and Virginia were pushed forward, to the proportional time period.
Political analysts say this will stop a movement or momentum candidate. You know, one of the people who gets a lot of attention and popularity at the start, but then fizzles out of the race and disappears.
The other major rule change is that a candidate must win eight or more states, to be eligible for the Republican nomination. In 2012, the requirement was five. Someone like Ron Paul, who won six states in 2012, no longer qualifies.