At nearly every event he has attended in Iowa over the past month, Sen. Ted Cruz (R-Tex.) has been asked about a very specific issue: ethanol.

Ethanol is emblematic of how a local concern can bubble up and affect a national political race. It has little resonance outside Iowa, but it has a huge bearing on a state that relies heavily on agriculture  -- and whose residents cast the nation's first votes for president. So what is Cruz's stance on ethanol, why is he being asked about it, and how could it influence his fortunes in this state's caucuses Monday night?

What is ethanol? 

Ethanol is a type of alcohol -- it's the thing in booze that makes you drunk. But it is also a fuel, which is what we're focusing on here. Ethanol is used as transportation fuel, either on its own or added to other fuels, such as gasoline. Much of the ethanol in the United States is made from corn. The fuel is big business here in Iowa -- 47 percent of the state's corn goes into ethanol, according to the Iowa Corn Growers Association.

How much ethanol is in fuel in the United States? 

The Renewable Fuel Standard (known as the RFS) was created by Congress in 2005. It requires that an increasing amount of biofuels, including ethanol, is mixed into the country's gasoline supply each year. Candidates, including Cruz, have noted that the RFS expires in 2022. But the mandate does not go away. Rather, the Environmental Protection Agency then sets the minimum levels of renewable fuels, not Congress.

What is Cruz's stance on ethanol? 

Here is the crux of the issue: Cruz takes a very different tack than almost all other Republicans campaigning here. He is against the RFS. Cruz decries the mandate as a Washington-driven, anti-free market scam that makes people rich.

"There's a reason the lobbyists want the people of Iowa focused on the RFS," Cruz said in Independence, Iowa. "Because as long as the RFS is front and center, it keeps Iowa dependent on Washington."

What does he want to do instead? 

Cruz has introduced legislation to end the RFS. He wants to stop what he says is the EPA's "blend wall," which has kept the amount of ethanol that can be blended into gasoline below 10 percent.

The blend wall is "keeping ethanol from expanding its markets," as it has done overseas, Cruz said.

The EPA had delayed the targets for how much biofuel should go into gasoline because of opposition from the petroleum industry. But in November, President Obama ordered refiners to mix 14.5 billion gallons of ethanol into gasoline, bringing the amount above the 10 percent threshold.

Cruz wants to do away with subsidies on all energy sources, leveling the playing field and allowing the market to dictate conditions and prices.

What do people in Iowa think of Cruz's position on ethanol? 

Cruz's stance on ethanol has been met with fierce opposition by some in Iowa. The state's Republican governor, Terry Branstad, has said Cruz should lose the caucuses because of his stance on ethanol and called him the "biggest opponent of renewable fuels." Cruz points out that Branstad's son is a pro-ethanol lobbyist (his group has been trailing Cruz in a Winnebago).

"His family makes a ton of money [from ethanol]," Cruz said of Branstad on NBC's "Meet the Press."

According to a poll by The Des Moines Register and Bloomberg Politics, 43 percent of those surveyed said they were bothered by Cruz's position on the RFS. Meanwhile, 77 percent of those surveyed said Branstad's comments about Cruz made no difference to them.

Most people who attend Cruz's rallies appear to agree with him -- even some Democrats.

Patty Timmens, a retired librarian from Cincinnati, Iowa, is a Democrat who came to hear Cruz speak in Centerville, Iowa, simply to ask him about ethanol.

"The ethanol thing is the only thing I actually agree with Senator Cruz on," Timmens said."He's the only one brave enough to talk about it in Iowa."

Many Republicans agree, too.

"Ending the subsidy is very important to me," said Van Hearn, an 86-year-old Republican in Centerville who plans to caucus for Cruz. "It makes everyone dependent on Washington."

But in tiny Ringsted, Iowa, a town of about 400 people near the Minnesota border, Kathleen Graves, a Democrat, needled Cruz on ethanol and Branstad's comments.

"I wanted to understand why he wants to abolish all subsidies," said Graves, a part-time farmer who said she came on her own to the event. "I'm sad that he wants do do away" with them.