US presidential election explained: What is the Iowa caucus?

On Monday night across Iowa, here in the American heartland, voters finally get to help choose the Democratic presidential nominee. It feels like the candidates have been campaigning for years for this moment. That’s because they have.

Iowa is the first state in the nation to vote for the man or woman who will challenge Donald Trump for the White House in November.

It’s a wonderfully personal form of politics, an election process known as a caucus. Part neighbourly persuasion, part Midwestern eccentricity, part hard-nosed campaigning, this is how it works:

We’ll know the result on Monday night. Four candidates are regarded as being in the top tier - Senators Elizabeth Warren and Bernie Sanders, the former Vice President Joe Biden, and a former mayor Pete Buttigieg.

Whoever tops this Iowa vote will have the key commodity - momentum - going into the next round of voting. New Hampshire is next and then it spreads out across the nation.

So Monday is an exciting day in the political calendar. After three tumultuous years of Donald Trump in the White House, Democrats are beginning down the road of voting for their candidate... and very possibly the next American President.