The national average price for diesel fuel in the United States topped $6 per gallon for the first time this Thursday, adding to already considerable pain at the pump ahead of the November midterm elections. The data comes from GasBuddy, which said in a statement that “As diesel climbs, higher supply chain costs work their way into the price of groceries, household goods, deliveries, and countless other products families rely on every day, even for households that never fuel a diesel vehicle.” Diesel prices in the U.S. are $2.30 higher…