The March 15 Republican primaries will be the most important contests to date in determining who the GOP presidential nominee will be. Donald Trump would be in a strong position if he sweeps Ohio, Florida, Illinois, and Missouri on Tuesday. But mixed results for Trump could make it difficult for him to get the 1,237 delegates needed to win the nomination. A look at the calendar shows that Trump's path to a majority isn't certain even if he does pull off a clean sweep on Tuesday.
What to look for on March 15?
You can pretty much ignore North Carolina, which has 72 delegates up for grabs but awards them on a proportional basis. The difference between coming in first place at 40 percent in North Carolina and second place at 30 percent is 7 extra delegates.
In pure winner-take-all contests of Florida (99 delegates) and Ohio (66 delegates), the candidate who finishes in first place will get all of the delegates.
It is also possible to rack up a lot of delegates in Missouri (52 delegates) and Illinois (69 delegates). Both states award a little more than one-fifth of their delegates to the winner of the statewide vote. Most of their delegates are awarded by congressional district to the candidate who gets the most district-wide votes.