As president, Mr. Biden has not yet challenged that logic. Instead, he visited an Iowa ethanol plant last year to boast about the lavish biofuels subsidies in his Inflation Reduction Act, and to announce a new waiver allowing more ethanol to be sold in the summertime to help suppress gas prices.

But his most important decision is still to come: What to do about the Renewable Fuel Standard that has kept the industry afloat since the mid-2000s.

The current standard requires 15 billion gallons of corn ethanol to be blended into U.S. gasoline every year. Since ethanol doesn’t make sense economically without the standard’s lucrative credits, America currently blends about 15 billion gallons a year. The standard was also supposed to mandate 21 billion gallons of so-called advanced biofuels brewed from grasses by 2022, farm wastes and other noncrop materials. But since they are hard to make economical even with the standard’s lucrative credits, only about a quarter of the quota was met in 2022.

The main exception has been 2 billion gallons of soy biodiesel, which Congress designated an advanced biofuel even though it’s made from crops, because Congress courts soybean farmers as slavishly as it does corn farmers. In fact, they’re mostly the same farmers.

But the rules and volumes that Congress created for the Renewable Fuel Standard only extended through 2022, and Mr. Biden’s E.P.A. could easily revise them to advance his climate goals. The agency could limit the standard to biofuels made from leftover restaurant grease, crop residues or other waste products that don’t use farmland. It could create a stricter cap on crop-based biofuels, as Europe has done. Or it could at least tweak its own approach to take land use more seriously in its emissions analyses. Crossing the farm lobby is never easy, but it can be done: Senator Ted Cruz of Texas chose not to kowtow to ethanol producers in the 2016 presidential campaign, and he still won the Iowa Republican caucus.

For now, the E.P.A.’s proposed rule would actually expand soy biodiesel, which is even more land-intensive than corn ethanol. And even though corn ethanol is basically moonshine, an ancient libation with a century-long history as a fuel, a bipartisan group of House members has also introduced a bill to reclassify corn ethanol as an advanced biofuel so it could finally blow past the 15 billion gallon threshold.

One co-sponsor, Representative Wesley Hunt, a Texas Republican, offered an amusing new justification for ethanol at a time when electric vehicles look like the future of transportation: “Congress must promote programs that encourage the internal combustion engine.” Back when internal combustion engines were new, congressmen with buggy-whip factories in their districts probably supported programs to encourage buggy whips. Change can be tough. Progress doesn’t always benefit everyone equally.