DES MOINES, Iowa – Potential 2016 Republican presidential candidates dove deep into agricultural policy on Saturday during lengthy question-and-answer sessions with a major Republican donor.

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In between advertisements pushing for the renewable fuel standard, potential presidential contenders including New Jersey Gov. Chris Christie, Wisconsin Gov. Scott Walker and former Florida Gov. Jeb Bush answered agribusiness mogul Bruce Rastetter’s questions about free trade, Cuba, genetically modified foods, the renewable fuel standard and immigration policy.

“No,” Christie said when asked if genetically modified foods should be labeled.

“None of us would build a house a put a fence around three sides of it and not on the fourth side,” Walker said when asked about immigration policy and border security.

view photo essay GOP hopefuls talk trade, immigration and more in Iowa Take a look behind the scenes of the Iowa Agricultural Summit, a major event drawing Republican presidential hopefuls.

“They’re like a pig in slop,” Bush said of the Environmental Protection Agency and government regulation generally.

Largely absent from the conversations on stage: Much of the rhetorical red meat that’s likely to characterize the Republican caucus contest here. Hillary Clinton’s use of private email while at the State Department went nearly unmentioned from the stage, where each GOP leader sat opposite Rastetter in a brown armchair, an enormous Sinclair tractor looming overhead.

The forum served as a test of each potential candidate’s ability to study up on the issues of key importance to Rastetter and those whose livelihoods are tied to farming–and agribusiness. A key issue: the renewable fuel standard, which helps sustain ethanol production here.

Texas Sen. Ted Cruz said he flat-out opposes the standard, calling instead for the preeminence of the free market. It’s a stance that could haunt him in a primary contest in this early voting state but one that’s earned praise from conservative grassroots groups in other parts of the country. Bush took a more nuanced approach, saying he supports the standard but that it should be phased out over time; he suggested 2022 as a possible date.

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Bush’s appearance at the summit was closely watched because it comes as part of his first visit to the state since announcing his interest in potentially running for president. He’s taken positions on immigration and education that could encounter resistance with the conservative electorate in Iowa.

“Immigrants who are here need to have a path to legalized status,” Bush told the Iowa crowd on Saturday, adding that no one is saying the 11 million undocumented immigrants in the U.S. “need to be rounded up and taken away.”

That position is distinct from supporting a path to citizenship for people who are in the U.S. without proper documents; that’s what the bill that passed the Senate in 2013 would have allowed. Florida Republican Sen. Marco Rubio was a key proponent of that bill and was originally supposed to appear at the summit. He ultimately canceled to attend a family wedding.

Politics did appear on the sidelines of the forum, where several of the potential candidates stopped to speak to reporters. Cruz called for a Justice Department investigation into Clinton’s use of a private email address and suggested that charges against New Jersey Democratic Sen. Robert Menendez were politically motivated and intended to punish him for opposing the White House.

“Barack Obama has become the president Richard Nixon always wished he could be,” Cruz said.