THE REPUBLICAN Party is holding its first caucus of the US presidential election in the state of Iowa tonight, where several candidates will vie to begin the serious build-up to the November ballot.

But what is a caucus?

The two main US parties use caucus meetings and primary elections to select a candidate to put forward for the presidential election.

Although a primary is an event at which party members simply show up and cast their votes, a caucus is much more a political rally than a voting procedure. Iowa is unique among the 50 states for holding caucus meetings instead of a straightforward primary.

How does it work?

Anyone registered with the party can attend the caucus meetings (several hundred of which will be held tonight across Iowa’s 99 counties this evening), but only those eligible to vote (ie over 18) can participate in the caucus ballot.

Anyone who wishes to speak in support of a candidate can do so at a caucus before voting for the candidates begins, meaning that campaigning is a big part of the event. It is important, then, that candidates have representatives at as many of the meetings as possible to continue to push for support.

A secret ballot is then held on the candidates who are seeking the party’s support. After being counted, the results from the caucus meetings across the state are reported back to the Republican Party’s headquarters and released to the public.

What happens next?

The caucus meetings and primary elections are part of a much wider process of allocating delegates to the candidates who are standing for their party’s nomination. The more delegates you have, the more likely you are to secure your party’s nomination.

Tonight’s caucus meetings will select delegates who will then go forward to Iowa’s county conventions (99 of them) in March, at which the Republican Party will choose delegates to go forward to the state convention.

Delegates who are selected through the state selection process (either by caucus meetings or primary elections) will meet at a Republican or Democratic National Convention to cast their votes in support of the respective candidates which leads to the selection of someone to run for the presidency.

Iowa has been the state with the first Republican and Democratic party caucus meetings since the 1970s and although it has had mixed success in predicting the eventual party nominees, it is considered the first real test for the candidates.

Political analysts believe it is hugely important for candidates to finish within the top three if they are to hold any serious hope of securing their party’s nomination for the presidency.