SHENANDOAH, Iowa — President Donald Trump won 93 out of Iowa’s 99 counties in the 2016 presidential race — the most for a GOP nominee since 1980 — thanks in no small part to local farmers. But now, farmers here are questioning if they'll vote for him again.

"Farmer tensions are running pretty tight out here right now,” Duane Aistrope, a corn and soybean farmer in Randolph, Iowa — roughly two hours southwest of Des Moines — told NBC News. "We got him elected out here in the Midwest — the farmers did."

The Midwest agricultural industry is up in arms not only due to the president's trade war, but because the Environmental Protection Agency recently exempted 31 small oil refineries from rules that would require them to blend ethanol, which comes from corn, into their fuel supply. Those exemptions are now forcing farmers to grapple with lost revenue from wasted crops.

Aistrope is one Midwestern corn farmer who, through the last two seasons, has battled depressed corn prices. Many farmers like him have stuck with Trump during his protracted trade war with China, arguing that the U.S. does need to fix its trade policy with Beijing. But now farmers such as Aistrope say these waivers are a step too far.

"Hopefully he’ll take care of us and do things right: Just uphold the laws for the ethanol industry that Congress put into place," Aistrope said.

The Renewable Fuel Standard is a law that requires the U.S. fuel supply to use a certain amount of corn ethanol in the country’s gasoline market to reduce greenhouse gas emissions and reduce the country’s reliance on imported oil, according to the EPA.

Corn makes up roughly one-third of crop produced in the U.S. and over the past several decades its production has steadily risen, according to the U.S. Department of Agriculture. Forty percent of total corn use in the U.S. is tied to growing ethanol production, according to the agency. And Iowa is among the top corn-producing states.

However, since Trump took office, his EPA has issued 85 exemptions to oil refineries to stop blending ethanol in their fuel — a staggering increase from previous administrations. The waivers have extended to giant oil corporations such as Chevron and Exxon. As a result, more than one dozen ethanol plants have shut down or halted production across the country this year.

Steam rises from the POET LLC ethanol bio-refinery in Gowrie, Iowa, on May 17, 2019. Daniel Acker / Bloomberg via Getty Images file

"Our demand has been destroyed by these small refinery exemptions, and that’s where we’re really focusing with the administration to say, 'Hey, look, you really have to fix this. Your EPA went too far,'" said Todd Becker, CEO of the Green Plains, a large ethanol production company that operates 13 corn ethanol plants in the region.

Becker says his company lost $150 million in profits in the last year. "The president has committed that he’s going to fix this for us, so we’re depending on that," Becker added.

As a result of the waivers, ethanol and corn prices have decreased 12 and 11 percent respectively, which could result in "a staggering $10 billion transfer of wealth from the agriculture and biofuel sectors to the oil industry," the Renewable Fuels Association, a trade organization, said in a statement last week. The organization also said that the waivers have reduced ethanol productions by 2.6 billion gallons and more than 2,500 jobs have been lost by recent closures.

On Thursday, the president tweeted about the ethanol industry, hinting that he would announce an aid package to help farmers. The president made a similar move for soybean farmers hit hard by his trade war with China.

The Farmers are going to be so happy when they see what we are doing for Ethanol, not even including the E-15, year around, which is already done. It will be a giant package, get ready! At the same time I was able to save the small refineries from certain closing. Great for all! — Donald J. Trump (@realDonaldTrump) August 29, 2019

Iowa Gov. Kim Reynolds and Iowa Secretary of Agriculture Mike Naig, both Republicans, sent a letter to EPA Administrator Andrew Wheeler last week urging the administration to reconsider the exemptions.

"The loss of these markets has taken a devastating toll on rural families facing one of the toughest years on record," they said. "Ethanol consumption fell for the first time in 20 years, commodity markets are depressed, and many biofuel plants, including several in Iowa, have already slowed or halted production."

Sen. Chuck Grassley, R-Iowa, an ally of the president, also excoriated the administration over the waivers.

"They screwed us when they issued 31 waivers compared to less than 10 waivers in all the Obama years," he told Iowa Public Television's "Iowa Press" earlier this month. "What's bad isn't the waiver. It's that it's being granted to people who really aren't (experiencing) hardship."

On the campaign trail during the 2016 presidential election, Trump said that he would defend the Renewable Fuel Standard and the biofuels industries’ roles in the marketplace.

U.S. Agriculture Secretary Sonny Perdue told farmers at an event in Illinois on Wednesday that the waivers were "disappointing" and that Trump believes the waivers are "way overdone," according to The Associated Press.

The president, earlier this summer, also announced to much fanfare in the Midwest that the administration would enact a rule change that would allow for the sale of E15, a more highly-concentrated fuel. But those working in the ethanol industry contend the oil refinery exemptions have negated those gains.

"A majority of farmers, whatever percentage that may be, supported Trump when he said he was going to take on China," Brent Renner, a farmer in Klemme, Iowa, told NBC News.

"So it’s hard to not have a sense of 'rah-rah' when you hear someone who is going to do that. The hindsight of all this is we think and wish it would have been handled in a different way without the use of food as a weapon in this trade war."

Vaughn Hillyard reported from Iowa, and Dartunorro Clark reported from New York. The Associated Press contributed reporting from Iowa.