DES MOINES, Iowa — Howard Dean took one bite of a deep-fried Oreo and dismissively pitched the rest into the garbage.

Mitt Romney famously flipped a pork chop, right into the gravel. And John Kerry capped his Iowa State Fair fare with a strawberry smoothie, rather than a cold beer that offered a chance for him to seem connected with regular folks.

“I wouldn’t order a smoothie,” said Jeff Link, a veteran Iowa Democratic operative. “That kind of summed the whole thing up right there.”

The state fair, a quadrennial presidential prerequisite stop, is a cultural obstacle course more fraught with pitfalls than opportunities to sway the narrow band of voters who will attend the state’s kickoff caucuses in less than six months. Starting Thursday, more than 20 Democratic presidential candidates will begin weighing nutritionally questionable food choices and navigating media flocks resembling crows on a French fry — all while trying to seem both presidential and comfortable with the folkways of Middle America.

This year, selections that include bacon-wrapped corn dogs and a monstrosity called the hot beef sundae pose particular challenges for Hawaii Rep. Tulsi Gabbard, a vegetarian, and New Jersey Sen. Cory Booker, who keeps vegan.

“There are few breakthrough moments, and the memorable ones are often not good,” said John Norris, who managed John Kerry’s 2004 Iowa caucus campaign.

Joe Biden, who will return to the fair Thursday, would know.

In August 1987, he lifted passages of a speech by British Labor Party leader Neil Kinnock’s speech without attribution during a 1987 Democratic candidates’ debate at the fair. The revelation punctuated previous questions of plagiarism that shadowed Biden and led ultimately to his early drop from the 1988 race.

It was an epic fair fail. But presidential history also is sprinkled with winning performances.

In 2007, Barack Obama’s romp through the Midway with his family — and iconic turn on the bumper cars with his daughter Sasha — cast a glow over the rising Illinois senator.

But for every such gauzy memory, there are more clunkers, or worse yet, permanent scars.

In 2007, amid heavy expectations, former Republican Sen. Fred Thompson famously made his Iowa debut by attending the Iowa State Fair wearing a pair of $500 Gucci loafers.

That was after he was chauffeured down the voter-packed Grand Concourse by golf cart to meet his escort, the notoriously frugal Iowa Sen. Chuck Grassley. Thompson stayed aboard the cart, waving only occasionally at the many star-struck voters who recognized him.

The episode was hardly a black eye. But, just as Kerry’s smoothie contributed to questions about the Massachusetts senator’s connection to regular folk, Thompson’s less-than-enthusiastic embrace of the time-honored Iowa tradition clashed with the down-home Southerner he often portrayed as an actor.

Some candidates this year may be better-prepared than others. Former Colorado Gov. John Hickenlooper will avoid Kerry’s oversight. Hickenlooper, who founded a successful brewery, will pour beers for fairgoers at the craft beer tent.