Only five states hold their contests on this day but it's significant because of the number of delegates are at stake. Not only are the states large - Illinois, Ohio and Florida, Missouri and North Carilina - and reward a lot of delegates but this is the first time in the primary that the winner is able to collect all the delegates from the state.
States voting before March 15 have to reward their delegates proportionally so theoretically every candidate can win delegates in one state.
