Republican presidential contenders will address a gathering of social conservatives in the early nominating state of Iowa but the event will be most notable for the 2024 candidate who will not be there – frontrunner Donald Trump.

Trump’s absence has rankled the organisers of the forum, Christian advocacy group The Family Leader, who argue the former president is blowing off an opportunity to court Iowa’s evangelicals, a key Republican voting bloc.

Iowa will hold the first Republican nominating contest on January 15, when voters will select their preferences to take on Democratic President Joe Biden in November 2024.

Candidates who received heavy evangelical support have won the state in recent years.

Florida Governor Ron DeSantis, former vice-president Mike Pence, former US ambassador to the United Nations Nikki Haley and US Senator Tim Scott will be among the candidates appearing at the forum, to be moderated by former Fox News Channel host Tucker Carlson.

Trump’s campaign said he had a scheduling conflict.

Doing it his way

DeSantis, who national polls show to be the most viable challenger to Trump, is relying on a victory in Iowa to turbo-charge his campaign and slow Trump’s momentum.

With a national poll lead of about 30 percentage points, Trump appears to want to engage with Iowa voters on his own terms.

After he was criticised for skipping the evangelical event, his campaign announced he would return to Iowa for a town hall next week.

The former president also made waves in Iowa this week by blasting the state’s popular Republican governor Kim Reynolds, suggesting she supports DeSantis despite a pledge of neutrality in the contest.

That led to The Family Leader’s president and CEO, Bob Vander Plaats, saying on Twitter that Trump going after Reynolds wasn’t smart and that the race in the state was “wide open”.

A former chair of the state Republican Party, Cody Hoefert, publicly stated he would no longer support Trump after his attack on Reynolds.

Reynolds is expected to appear at the forum on Friday and sign the six-week abortion ban passed this week by the Iowa legislature.

Trump has criticised such restrictions as being politically divisive.

-AAP