Republican 2016 presidential candidates have taken to the debate stage in Iowa, with the notable exception of frontrunner Donald Trump.
He decided to withdraw after Fox News refused to drop host Megyn Kelly, whom Mr Trump accused of bias.
The debate began with his rival Senator Ted Cruz marking his absence by throwing mock insults at the others.
The billionaire businessman is holding a charity rally nearby, in honour of the country's war veterans.
Voters in Iowa on Monday are due to pick their presidential nominee for each party.
In making his decision to skip the main debate in Des Moines, Mr Trump claimed "unfair" treatment from Ms Kelly of Fox News, which is hosting the debate in Iowa's state capital, Des Moines.
The Republican field is a wide one, and a debate undercard featuring four of the lowest-polling candidates was held earlier on Thursday evening.
In polls, Mr Trump is currently leading the Republican pack in Iowa with 33.2% of the vote (6.5 percentage points above his nearest rival, Texas Senator Ted Cruz), and is in the lead nationally with 36.2% (16.8 points over Mr Cruz).
The Iowa caucuses on Monday are seen as the first real test of the election campaign, and the beginning of a series of state-by-state contests to chose delegates for both Republicans and Democrats.
Unlike a primary, which is a traditional election featuring secret ballots on polling day, the caucuses in Iowa is a meeting of registered party voters and activists where they discuss the candidates and then vote.