The final showdown: Republican National Convention explained

Republican presidential candidate, Donald Trump holds a plane-side rally in a hanger at Youngstown-Warren Regional Airport in Vienna, Ohio, Monday, March 14, 2016. (AP Photo/Gene J. Puskar)

Donald Trump has warned of "riots" if power-brokers deny him the nomination at the convention. So what exactly is the Republican National Convention?

Q What is the Republican National Convention?

A The gathering, in July, at which the party officially nominates a candidate for president. In recent years it has been a mere formality.

Q Why is this year different?

A With Donald Trump's loss in Ohio, it is highly likely that he will arrive without the majority needed to win outright. That would set in motion the first contested convention since 1976. Republican power brokers are plotting to wrest the nomination from Mr Trump's grasp, and put forward a more palatable alternative at the convention.

Q What is a contested convention?

A It is when no candidate enters the convention with a simple majority. A candidate is then officially nominated when they gain a majority of the delegates voting at the convention. For the first ballot, most delegates are committed to repeat the way they voted in the state primaries. On subsequent ballots most are unbound, and can shift to a candidate of their choice. Those who backed candidates who have since dropped from the race, most notably Marco Rubio, will be unbound on the first ballot, and could provide Mr Trump the majority he seeks or prevent him from achieving it. Should subsequent rounds fail to produce a winner, the delegates can - at least in theory - keep on voting indefinitely, although a nominee must be selected before the four-day convention is over.

Q Could someone who hasn't run in the primaries win nomination?

A For Mr Trump to be overtaken, the delegates would have to coalesce behind one of his remaining rivals, or a "white horse" candidate whose name can be entered at the convention itself.