WASHINGTON — Sen. Joni Ernst said Thursday that President Donald Trump should replace Environmental Protection Agency Administrator Andrew Wheeler if he fails to deliver on promised levels of federally mandated ethanol blending.

The Iowa Republican made her comments after the EPA released the final version of new ethanol rules, which falls short of the regulatory certainty the biofuels industry and its allies have sought.

Ernst said the administration has promised that 15 billion gallons of ethanol will be blended into the nation’s fuel supply annually going forward.

Ernst mug (copy)

Joni Ernst

“If we’re not seeing that, then yes, the president needs to make a change,” Ernst said. “Then the president needs to find somebody else to work for him at EPA.”

It’s the latest chapter in a long-running dispute between oil and gas interests and the biofuels industry. Trump has tried — thus far in vain — to make both sides happy.

The decision is fraught with political implications, as it pits two Trump constituencies in key electoral battlegrounds against each other — rust belt refinery workers on one side and Midwestern grain farmers on the other.

At issue is the Renewable Fuel Standard, which requires refineries to blend a certain amount of corn-based ethanol and other biofuels into the fuel supply every year. The Trump administration has been granting exemptions to refineries at a pace ethanol backers say substantially reduces demand for their product and has idled ethanol plants.

Biofuels advocates coalesced around a plan to account for the lost gallons based on a three-year rolling average of refinery waivers.

But the EPA went with a plan that relies on averaging Department of Energy recommendations. The biofuels industry says the EPA has made a habit of ignoring those recommendations.

Ernst and Sen. Chuck Grassley, R-Iowa, issued statements criticizing the finalized rules.

Ernst said the EPA missed an opportunity to “restore the broken trust of farmers and to follow through on the president’s commitment.” Grassley said he understands “the hesitation from Iowans to trust the word of EPA to actually follow through on that commitment.”

Sen. Deb Fischer, R-Neb., said in a press release that the final rule is an improvement over a previous version but that she understands Nebraskans are wary of the EPA.

“President Trump cares about farmers and has made big promises to rural America,” she said. “I will continue to work to make sure those promises are fulfilled.”

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Nebraska Gov. Pete Ricketts and Iowa Gov. Kim Reynolds, both Republicans, issued statements vowing to hold the EPA accountable.

Monte Shaw, executive director of the Iowa Renewable Fuels Association, said in a press release that the EPA’s chosen approach means that the market can’t be sure what the actual blending levels will be until well into the future.

“Instead of certainty, we are essentially being told to trust the EPA to uphold the RFS in the future even though for the past three years the EPA has routinely undermined the program,” he said. “Every farmer and biofuel supporter I have talked to is deeply disappointed, frustrated, and quite frankly angry. I don’t think the White House truly understands the depth of discontent in farm country.”

It’s not clear that the new rule will satisfy refiners, either.

The Fueling American Jobs Coalition, which represents refineries and gasoline stations, issued a statement saying the RFS has been exposed as merely another subsidy for agribusiness companies, one that is zealously guarded by home-state politicians.

The entire concept of reallocating exempted gallons is flawed and will prompt court challenges, the group said.

“It will not go unnoticed that the administration has broken its promise to protect manufacturing workers in Pennsylvania, Ohio, Texas and across the nation,” the statement said.

The move will also renew questions about the underlying value of the mandate, the group said.

“And just as sure as the sun will rise tomorrow over Iowa, biofuels interests will be back next year to ask for even more,” it said.