What’s fueling inflation? Fuel.

The final CPI report before the midterms is expected to reflect soaring energy costs compounded by higher airfares, pricier iPhones and rising car prices.

Inflation in America is being powered by diesel. The price of the fuel, used by farmers and truckers, is up more than 75% since the start of the Iran war in late winter. Diesel costs have become a particular concern for economists, who say higher diesel fuel costs trickle down into “just about everything.” And the final government inflation report before November’s pivotal midterm elections will most likely reflect how much of a headache it has become for businesses and consumers. The Bureau of Labor Statistics is set to release its September consumer price index report at 8:30 a.m. Wednesday. It’s expected to show the annual rate of inflation rose to 3.7% from 3.4%, according to a survey of economists from Dow Jones.

From August to September, prices are expected to have risen by 0.6%. The monthly jump, if it is confirmed, would also be one of the largest in years. Since August, oil prices have risen to more than $105 per barrel from about $80. The price of regular gas, which most consumers buy, also remains elevated by more than 45% since late February, when the Iran war was launched. As early voting kicks off this week, a higher inflation reading would come at a precarious moment for Republicans defending majorities in the House and the Senate. Polls consistently