The U.S. national average price of diesel on Thursday surpassed $6 a ​gallon for the first time ever, according to price tracker GasBuddy, as the U.S.-Israeli war on Iran and Ukrainian attacks on Russia’s refineries have squeezed supply.

Diesel ‌fuels trucks, trains, ships and heavy equipment that keep global supply chains moving. It is also crucial to running farm equipment.

The latest surge in fuel costs is adding to inflationary pressures that have already strained consumers and businesses this year, creating a political headache for Donald Trump and Republican lawmakers as they seek to defend thin congressional majorities in November’s midterm elections.