The battle for the US presidency shifts into a new gear with the start of states' caucuses and primary elections in February 2016, beginning with the Iowa caucuses on Monday and followed by the New Hampshire primary on February 9th. Candidates on both sides of the political divide face fierce competition this year, and it could take until well into the primary season before a clear nominee has emerged for both the Democrats and Republicans. So how do these contests work?
What are the primaries and caucuses for? They are the way the United States chooses its presidential nominees and will continue, state by state, until June, before July's Republican and Democratic party conventions. These idiosyncratic contests have evolved over time, rather than being stipulated in the US Constitution, and involve voters determining the affiliations of delegates their states will send to national party conventions, where the final nominee is anointed. The rules governing them are complex.
What is the difference between a primary and a caucus? Caucuses used to be a common way of choosing nominees, but now only a handful of states, including Iowa, Alaska, and Nevada, rely on them. Primaries are more widely used and are like typical elections, with polls open all day and people turning up to cast their ballot.
Caucuses are quirkier affairs in which voters assemble for meetings in schools, churches and community halls. Turnouts in caucuses tend to be much lower and frequented by relatively narrow groups of enthusiasts and ideologues. For example, in 2008 Barack Obama, the winner of Iowa's Democratic caucus, received the votes of just 4 per cent of the state's eligible voters, according to a Harvard Kennedy School study.
How consistent are the rules? The rules vary not only from state to state, but also between the two parties. Some states' contests are only open to registered party members, for example, while others are open to all eligible voters – and there are variants in between. In Iowa the Republican Party holds secret ballots at its caucuses, whereas the state's Democrats conduct far more elaborate rituals in which attendees publicly signal their preferences by congregating in designated locations. If a candidate fails to meet a 15 per cent threshold at the event, his or her supporters are then wooed by other contenders, as are undecided attendees. Caucus results determine which delegates are sent to county and then state conventions, which in turn determine the delegates at the national convention.
So how do the results drive the eventual nomination? The modern presidential nominating process was ushered in following the chaotic 1968 election between Richard Nixon for the Republicans, Hubert Humphrey for the Democrats and the independent George Wallace, with the goal of democratising the process and ending jockeying by party elders.
The final nomination is meant to be firmly anchored to the outcomes of the state primaries and caucuses. This means that the result is normally clear by the time of the summer conventions. However, the link between state results and the exact number of convention delegates is not easy to follow.
For the Democrats, delegates are allocated under a proportional system, with a cadre of unpledged delegates informally called "superdelegates" who have the potential to swing the result, presumably in favour of an establishment candidate such as Hillary Clinton.
The Republicans allow states more latitude in allocating delegates, says Joshua Putnam, a lecturer at the University of Georgia. The latest Republican reforms require states to follow a broadly proportional allocation during a two-week window in early March, after which they can shift to a winner-takes-all system or some sort of hybrid.
So is the party convention a mere formality? Normally yes, but not automatically. The Republican contest in 1976 was still undecided at the time of the convention at Kansas City, where Gerald Ford eventually prevailed over Ronald Reagan. Since then a clear winner has always been apparent by the time the conventions come around.
The turbulent contest on the Republican side this time has led to speculation that there will be a contested convention in July, in which an inconclusive first tally leads to multiple rounds of balloting and intense dealmaking. Delegates may become free agents in these later rounds. The Republicans are holding their convention in Cleveland, Ohio, from July 18th-21st, while the Democrats' convention will be in Philadelphia from July 25th-28th.
How important are early results from Iowa and New Hampshire? Iowa and New Hampshire are outliers: relatively small states with far lower unemployment rates than the national average and predominantly white populations, suggesting they are far from representative of the concerns of the broader US population. Yet the two states garner (and relish) huge global attention given their vociferously defended positions at the start of the electoral calendar.
Advocates argue the intense campaigning in the two states allows local voters the opportunity to examine candidates much more closely. A candidate who wins either contest and then moves on to poll well in South Carolina and Nevada would go into the all-important flurry of contests on "Super Tuesday" on March 1st with enviable momentum. In almost every race for the past 36 years, each party's eventual nominee has won either Iowa or New Hampshire.
How much weight should be put on the opinion polls? Past elections have shown how badly awry polls can go. In the January 2008 New Hampshire primary, all 13 polls in a final round of pre-election surveys predicted an Obama win, only for Hillary Clinton to emerge as victor. This year's polls will provide plenty more grist for the critics. Take the issue of sample sizes. In New Hampshire in 2012 the average pool of Republican voters interviewed was 590, according to a Financial Times analysis of data collected by Real Clear Politics. So far this year it stands at 490. The result is less precise polls.
Key states: when they vote
February 1st: Iowa
February 9th: New Hampshire
March 1st: "Super Tuesday". Fourteen states vote, including Colorado, Virginia and Texas
March 15th: Six states vote, including Florida, Illinois and North Carolina
April 5th: Wisconsin
April 19th: New York
April 26th: Maryland and Pennsylvania
June 7th: California and New Jersey
Copyright The Financial Times Limited 2016