A post-Super Tuesday guide to how the remaining US primaries will be won

Once the results of a state’s primary election are known, parties allocate delegates to a national convention for each presidential candidate based on their share of the vote. A candidate with more than 50% of delegates overall (1,237 for Republicans or about 2,383 for Democrats) officially wins the party’s presidential nomination. Therefore, the race is decided by the number of allotted convention delegates, not by the number of votes in each state election. Exactly how delegates are distributed can differ widely from state to state, however. Nearly all primaries so far have allocated proportionally, but the remaining states use a range of different systems.

REPUBLICANS

The Republican candidates must navigate a complicated field of variously structured primary contests if they hope to capture the nomination.

The three most decisive types of contest that states use to determine who (if anyone) gets to the winning 1,237 delegates are:

METHOD 1. Seventeen states award 519 delegates to the statewide winner. The most important of these are Florida (99 delegates available) and Ohio (66), the home states of Senator Marco Rubio and Governor John Kasich, respectively, both of which vote on March 15th.

METHOD 2. Six states award a set of delegates to the winner of each of their congressional districts (287 in total), in addition to any delegates they award the statewide winner. Most notable among these states is California (among the last states to vote).

METHOD 3. Eight states award 225 delegates to statewide majority winners (i.e. a candidate who wins 50% or more of the vote); if no candidate wins 50%, they allocate delegates proportionally. Three states allocate 123 delegates to candidates who win a majority in congressional districts.

Other states

Thirteen states use other methods to allocate delegates—mostly either a proportional system (like New Mexico) or a convention (like Colorado). Proportional systems tend to give only small margins to their winners, while the few convention states are small and hard to predict. A few states elect their delegates directly. A handful also send delegates to the convention “unpledged”, meaning they are not required to support a given candidate. In the event that one candidate narrowly misses a majority, expect these delegates to come under heavy pressure.

DEMOCRATS

The race for the Democratic nomination is more straightforward: all states allocate pledged delegates proportionally, about two thirds in districts and the rest statewide; as a result, it can take a while for the race to conclusively resolve (as in 2008). Unlike the Republicans, Democrats have a large pool of “superdelegates”—mostly senior party officials and members of Congress—who aren’t determined by the primary process and may support any candidate.

*Congressional districts are electoral constituencies that elect a single representative to Congress. They are apportioned to states by population. All states have at least one; California has the most (53).

Sources: The Green Papers; The Economist