The butter cow is carved. The pork chops are prepped. And the candidates who weren’t at the Iowa State Fair on Thursday are on their way.

Six candidates for the Republican presidential nomination will be circulating through the fairgrounds on Friday, as they try to woo voters months ahead of this crucial first nominating contest.

A day at the fair — one of the largest in the nation — has long been one of Iowa’s quirkiest political traditions. Presidential aspirants make their campaign pitch but also flip pork chops at a grill sponsored by the state’s pork industry, pay homage to a sculpture of a cow made of 600 pounds of butter and eat their share of fried foods — all while navigating hecklers and a media throng.

It doesn’t always go as planned: In 2007, Mitt Romney flipped his chop into the gravel. (He lost the caucuses that year but won the party’s nomination four years later.) And in 2015, Donald J. Trump, walking through the fair in a navy blazer and buffed white dress shoes, offered rides at random to handfuls of Iowa children in his helicopter parked nearby. (He, too, lost the caucus but won the nomination.)

Five months before the 2024 caucuses, Iowa has already emerged as a make-or-break contest in this race. With Mr. Trump leading by a double-digit margin, the state represents the best opportunity for his rivals to stop his march to the nomination. If one of them can take him down — or even come close to beating him — it would show cracks in his support and potentially undercut the narrative that he still has a stranglehold on the Republican base. If Mr. Trump wins in Iowa, party strategists say, it will be difficult to slow his momentum, particularly as the race broadens out to states across the country.

Friday’s lineup at the fair is a list of Republican candidates who have been struggling to break into the top tier of the nomination race, including former Vice President Mike Pence, former Gov. Nikki Haley of South Carolina, Gov. Doug Burgum of North Dakota, Mayor Francis X. Suarez of Miami and Larry Elder, the conservative commentator.

Several candidates are scheduled to deliver speeches at the political soapbox, a small podium open to the public and sponsored by the Des Moines Register. Others will participate in public Q. and A. sessions with Gov. Kim Reynolds of Iowa, opting for a more scripted encounter with a fellow Republican.

While Saturday will bring Mr. Trump and Gov. Ron DeSantis of Florida to the event, the Friday attendees are likely to enjoy a day basking in the Iowa attention without the former president stealing the show.