U.S. President Donald Trump launched an effort on Tuesday to increase ethanol use in the nation's gasoline pool, delivering a long-sought political victory to the country's Farm Belt and angering oil refiners ahead of November's congressional elections.

Reuters reports that the president announced the lifting of a ban on summer sales of gasoline blended with 15 percent ethanol, known as E15, at a closed-door meeting at the White House, Republican senators told reporters after the meeting.

"My administration is protecting ethanol. ... Today we are unleashing the power of E15 to fuel our country all year long," Trump told a cheering crowd of supporters at a rally in Council Bluffs, Iowa.

The announcement capped a months-long effort by the White House to thread the needle between rival corn and oil industry interests, by boosting ethanol demand while also cutting costs for refiners. In the end, Trump is moving ahead without the support of the oil refining industry, which wanted more in return for agreeing to lift the summer ban.

The move is also aimed at helping the political fortunes of Republican candidates in the Midwest saddled with a tough farm economy and the imposition of import tariffs by Trump and China. Polls show close election races in Iowa for the governor's seat and two congressional seats.

Trump told the rally that Democrats would "end ethanol" if given the chance. "You'd better get out there and vote for Republicans," he said.

Nancy Pelosi, the top Democrat in the U.S. House of Representatives, said in a statement: "Democrats remain vigilant to ensure that this new measure will create real benefits for America's farmers."