DES MOINES, Iowa (AP) — Sen. Joni Ernst says she’s pushing EPA Administrator Andrew Wheeler to fulfill the promises the president has made to blend a mandated 15 billion gallons of ethanol into the nation’s fuel supply.

Ernst says she’ll call for President Donald Trump to fire Wheeler if the EPA doesn’t meet those blending promises.

Like other Iowa Republicans, Ernst has criticized the EPA but rarely Trump when questioned about the administration’s granting of oil refinery exemptions from blending ethanol into gasoline. That has removed 4 billion gallons of corn-based ethanol from the market, angering farmers.

Speaking to Iowa reporters Thursday, Ernst laughed when told Trump on Wednesday told the natural gas industry in Pittsburgh that Wheeler was working with small refineries to “give them everything they need” to stay in business. Trump applauded Wheeler as doing a “fantastic” job.

When asked if she would hold Trump responsible if the administration doesn’t meet his promises, Ernst said she’d watch the EPA and seek Wheeler’s firing if less ethanol is blended.