Former president Donald Trump plans on Friday to headline his largest Iowa campaign event in nearly four months with a speech to thousands at an arena in the western part of the state. Trump will use his appearance in Council Bluffs on Friday afternoon to attack his top GOP rival, Florida Gov. Ron DeSantis, for opposing the federal mandate for ethanol, a renewable fuel additive that Iowa leads the nation in producing. “DeSantis has problematic policy positions that hurt farmers and demonize ethanol,” Trump spokesperson Steven Cheung told The Associated Press ahead of Trump’s visit. “President Trump plans to highlight that.” The large Republican presidential field has spent a lot of time over the last few months in Iowa, the leadoff GOP caucus state. In June, more than a half dozen candidates, including DeSantis, former Vice President Mike Pence, former United Nations Ambassador Nikki Haley and US Sen. Tim Scott of South Carolina, attended Sen. Joni Ernst’s annual “Roast and Ride” fundraiser that kicked off a busy summer campaign season. Trump campaigned in the Des Moines area last month, meeting with GOP state lawmakers, influential conservative pastors, campaign volunteers and a suburban Republican breakfast club. That visit came about a week before he was indicted on federal charges stemming from classified records he kept at his Florida home. Before Friday, his last large event in Iowa was in March, when he spoke to more than 1,500 people at a theater in Davenport and also went after DeSantis on ethanol. He was due to hold an outdoor event in May in Des Moines with about 5,000 attendees expected, but his campaign called it off because of bad weather. Although caucus campaigns have become more focused on national party priorities over the past two decades, some candidates have continued to portray support for ethanol – specifically the federal mandate that the nation’s fuel supply contain a minimum volume of renewable fuels – as a litmus test in Iowa. As a congressman from Florida, DeSantis co-sponsored a bill in 2017 that would have immediately ended the renewable fuel standard, a position consistent with fiscal conservatives who see such mandates as government overreach. As a candidate, Trump has promoted the executive order he signed as president increasing the retail sale of fuel containing 15% ethanol. Recent history, however, suggests a lack of support for ethanol may not be disqualifying. In 2016, Texas Sen. Ted Cruz, who opposes the mandate, won Iowa’s Republican caucuses, handing Trump an early defeat in his ultimately successful White House campaign.