Republican presidential candidates made sure that they played to their audience at the conservative Family Leadership Summit in the key state of Iowa on Saturday – but as the large media contingent showed, they had a broader target in mind.

The Family Leadership Summit is supported by organisations including the Conservative Review, Christians United for Israel and the National Organization for Marriage. Big names from the world of politics ensure a large turnout – last year's event drew around 1,200 conference attenders and 100 media representatives, while this year numbers were expected to be 2,700 and 130 respectively.

The white evangelical vote is particularly significant for Republicans and the candidates were keen to stress their distinctiveness not just from President Obama, who came under fire for his policies towards Islamic State, Iran, same-sex marriage and global warming, but from each other.

A Bible was placed on the table next to the candidates, who addressed the crowd and faced questions from the moderator, Fox News contributor and political consultant Frank Luntz.

Florida's Senator Marco Rubio picked it up and read from Luke 12:48, "From everyone who has been given much, much will be demanded; and from the one who has been entrusted with much, much more will be asked." He was scathing about Obama's terrorism policy, saying: "I'm sure he's against it, I know that he is, but he won't call it what it is, and he won't confront it in a meaningful way."

Former senator Rick Santorum said he would make saving the institution of traditional marriage his priority if elected president: "Instead of spending our bully pulpit time on global warming, we will spend it on trying to nurture children and raising healthy and happy families."

Louisiana's Governor Bobby Jindal said the next president should protect businesses that refuse to compromise their religious views on traditional marriage. "The government should not be able to fire me, take away my tax status or discriminate against me for being a Christian," he said, receiving a standing ovation from the crowd.

Senator Lindsey Graham called for a measure of bi-partisan working, saying: "To the 100 per centers out there, how do you save the country from becoming Greece without getting a Democrat to help you? I don't know how to do that." Like the others, he used strong language about Islamic State, saying: "These are religious Nazis. They can't be dealt with. They have to be degraded and eventually destroyed. ...We're going to rebuild our defenses and go after these b*****ds and kill every one of them if we have to. There is no other way to do it."

Former Texas governor Rick Perry made sweeping criticisms of the Supreme Court regarding its same-sex marriage ruling, saying: "I don't think we can take any chance of having individuals put on our Supreme Court without them having a clear understanding of their constitutional roles as justices." It was a theme also taken up by Mike Huckabee, who received standing ovations and loud applause throughout.

Senator Ted Cruz pledged to "cut off every penny of taxpayer funding" for Planned Parenthood affiliates, following the release of a shocking video in which an executive discussed the alleged sale of body parts from aborted foetuses.

Wisconsin Governor Scott Walker also addressed the controversy, saying: "There's a lot of people who come on stages like this and make great speeches about how they're going to fight to defund Planned Parenthood. I've actually done that [as a governor]. And if I'm given the chance of being president, I'm going to continue to be a pro-life president just like I've been a pro-life lawmaker, pro-life county executive and pro-life candidate for many years to come."

Ben Carson called for government cuts but pledged support for the military. He urged action against Islamic State, including economic sanctions and taking their land and their oil wells.

The biggest headlines, however, were generated by Donald Trump, who said that Vietnam veteran Senator John McCain was only seen as a war hero because he had been captured. "He's a war hero because he was captured," he said. "I like the people who weren't captured." He was roundly condemned by other candidates. Trump was asked whether he ever asked God for forgiveness, and said that he didn't: "I just go on and try to do a better job from there. I don't think so. I think if I do something wrong, I think, I just try and make it right. I don't bring God into that picture. I don't."

The highly conservative policies advocated by the candidates went down well with their audience in Ames. However, while white evangelicals disproportionately vote Republican, other demographic factors mean that the successful candidate for the nomination will need to expand his appeal beyond the core vote in order to beat a Democrat nominee.