Evangelicals have made up more than 60 percent of GOP caucus-goers in past years, and helped catapult former Arkansas Gov. Mike Huckabee to the top tier in 2008. 

If one of the candidates can get these voters to rally around his or her candidacy this weekend, it would be a major boost to that campaign and could act as a springboard to the top tier in Iowa.

At the event, former House Speaker Newt Gingrich (Ga.) and businessman Herman Cain will seek to shore up their standings in the polls, and might have to address questions about their faith as well as about past infidelities (Gingrich) and allegations of sexually inappropriate behavior (Cain).

Rep. Ron Paul (Texas) will look to boost his social-conservative bona fides on the abortion issue, but will also have to discuss his view that gay marriage should be decided by the states. 

If former Sen. Rick Santorum (Pa.), Rep. Michele BachmannMichele Marie BachmannYes, condemn Roseanne, but ignoring others is true hypocrisy Bachmann won't run for Franken's Senate seat because she did not hear a 'call from God' Billboard from ‘God’ tells Michele Bachmann not to run for Senate MORE (Minn.) and Texas Gov. Rick Perry hope to gain traction in the state, they desperately need to unite social conservatives, their natural base of support, behind them. 

“The Vander Plaats event Saturday is big — there’s an awful lot of social conservatives who’ve stayed out of the election process thus far, are engaged in the process but haven’t picked who they’re going to work for,” said Craig Robinson, a former political director of the Iowa Republican Party. “This could be the day a lot of them make the decision on who to support.”

The Branstad event isn’t as high-stakes for the candidates, but the attendee list shows who’s taking Iowa seriously — and who isn’t. All of the major GOP candidates besides former Massachusetts Gov. Mitt Romney and former Utah Gov. Jon Huntsman will be there.

Branstad has avoided taking sides in the race and said he won’t endorse a candidate this election. But after Romney’s campaign announced the candidate would not attend Branstad’s birthday fundraiser, Branstad blasted Romney’s approach to campaigning in Iowa.

“I think he’s making a big mistake by not coming here and spending more time,” Branstad said earlier this week. “I mean, Romney is dropping in the polls, and I think he wants to keep down expectations. Well, his expectations may get really bad if he doesn’t get a little more serious.”

Romney and Huntsman have banked their campaigns on doing well in New Hampshire, the first-in-the-nation primary state.