When the Iowa Faith & Freedom Coalition plays host to nine Republican White House hopefuls this weekend, the conservative Christian group will simply be pursuing its stated mission to "take back our state and country".

But the Republican contenders who will speak at the group's annual Spring Kick-Off face a more delicate balance: How to address pressure from the Christian group to toe the conservative line on a number of social issues such as abortion and gay marriage without alienating members of the broader party who are more focused on the economy or foreign policy.

Iowa holds the country's first nominating contests with its caucuses, giving the small, Midwestern state an outsized role in the presidential scrum. But winning the hearts and votes of the farmland state's large conservative bloc is not enough.

"Certainly Christian conservatives will be up to half of all the likely caucus goers," said Doug Gross, who chaired Mitt Romney's 2008 Iowa campaign. "You can't ignore what they care about."

But, he added, no candidate will be able to win the nomination on their backs alone. "You have to include them without letting them be your only source of support," he said.

Without a broad coalition of voters, many with different priorities or expectations, Republican hopefuls could find themselves locked out of the party nomination and thus the presidency.

The lineup underscores the importance of the Iowa event: Florida Senator Marco Rubio and Wisconsin Governor Scott Walker, both spoken of as top-tier Republican White House aspirants; Senators Rand Paul and Ted Cruz, and evangelical favourites Mike Huckabee and Rick Santorum. Others on the agenda are Rick Perry, Governor Bobby Jindal and Carly Fiorina.

However, two high-profile Republicans who are expected to seek their party's nomination, former Florida Governor Jeb Bush and New Jersey Governor Chris Christie, will not be in attendance.

Candidates who do well in Iowa – especially against expectations – can find themselves gaining a powerful boost as they move on to campaign in other states.

Christian conservatives have been a reliable voting bloc for Republicans. In the 2014 House elections, 78 per cent of white evangelicals voted Republican, according to Pew Research.

But determining how big a role evangelicals play in the party is difficult, with inconsistent research numbers, shifting attitudes nationally on social issues and changing US demographics.

On gay marriage, for example, in 2001, only 35 per cent of Americans supported same sex marriage, according to Pew Research polling. In 2014, 52 per cent supported it.

But according to Reuters/Ipsos polling data, 61 per cent of likely voters in Republican primaries oppose gay marriage.

"Where the Christian conservatives get into trouble ... is when they attempt to be exclusive, where you either share my world view or you're going to go to hell. That's not the approach you can take," said Gross."

US Census numbers underscore changes in the voting population. The Census Bureau projects that the United States will become a majority-minority country by 2043, with no single racial group in the majority.

Still, social conservatives say they're aware that a range of issues will matter to voters in the 2016 election, and that no single candidate will likely give them everything they want.

"There's no candidate that can fix everything immediately," said Connie Schmett, a longtime Iowa Republican activist who plans to be at Saturday's event.

But social issues will dominate on Saturday, with questions on the economy and foreign policy receding, at least for the evening.

"Faith and freedom folks, its title sort of discloses the content," said Richard Schwarm, a former Iowa Republican Party chairman.