This election cycle, the Republican National Committee compressed its calendar. In 2012, the primary season began in early January; this time around, it starts in February. In 2012, just 72 percent of delegates were allocated by May 8; this time around some 85 percent of all delegates will be allocated as of May 10. Still, not everything has changed: California’s June primary remains the bookend of the process, as it has been for decades.
Importantly, states that hold their primaries or caucuses before March 15 must allocate their delegates proportionally (although they are allowed to mandate a minimum threshold of support). A candidate might therefore rack up a significant number of primary “wins” without building up much of a lead in delegates. That could give the trailing candidates a strong incentive to hang around (assuming they still have enough money to campaign) in the hopes of surging when the contests largely switch to winner-take-all. The opportunity for huge delegate bounties really begins on March 15: At that point, more than half of the delegates will still be unallocated, so a late-breaking candidate could increase his delegate count quickly.
Something else to keep in mind is that some states allocate portions of their delegates as winner-take-all by congressional district. This could be quite important and generate surprising results, in that it effectively gives a boost to Republican voters in heavily Democratic districts, where turnout in GOP primaries is correspondingly low.