A potential new inflation headache is forming from the Strait of Hormuz to America's farm fields — threatening to ripple into food supply and grocery prices months from now. Why it matters: The Iran war could reignite the one form of inflation voters feel most directly — in the grocery aisle — just as midterm campaigns ramp up.The big picture: Not long after our last bout of food inflation — caused partly by the increase in commodity prices from the outbreak of the Russia-Ukraine war — we're staring straight in the face of a similar chain reaction.The Strait of Hormuz — which has been effectively shut down due to disruption from the war — ferries about one-fifth of the world's oil and about 25%-35% of fertilizer material, according to Morningstar.That disruption has already triggered a spike in the price of oil and fertilizer, which could undermine agricultural production, leading to higher prices of groceries and restaurant food.Threat level: The American Farm Bureau Federation warned in a letter to President Trump that "supply chain shocks are expected to drive already record-high input prices even higher."Farmers fear losing access to key materials such as urea, ammonia, nitrogen, phosphate, and sulfur-based products.Shortages could come just as the all-important spring planting season is about to begin. "This risk is not hypothetical," said Angela Huffman, president of ag watchdog group Farm Action, in a letter to Trump. "With renewed geopolitical instability now impacting fertilizer shipments, there is a real risk of a repeat."By the numbers: Gulf states now menaced by war produce nearly 49% of the world's urea, a critical solid nitrogen fertilizer, and about 30% of ammonia, according to AFBF.And the U.S. gets about 97% of its potassium from foreign sources, plus 18% of its nitrogen and 13% of its phosphate.What they're saying: "Fertilizer's not an option to farmers — it's a critical input that determines the crop yield and ultimately the food supply for the American people," AFBF president Zippy Duvall said on a conference call."It's not just a farm issue — it's a food security issue and an economic issue for the entire country," Duvall said. "When farmers face supply shortages or price increases, those impacts ripple through the entire food chain."The Trump administration "is supporting farmers through unprecedented international market access, lowered taxes, and improvements to the farm safety net," a U.S. Department of Agriculture spokesperson says."President Trump is utilizing all the tools available to ensure farmers have what they need to continue their farming operations - emphasizing the long-term gains will far outweigh any short-term disruptions."Zoom out: The fertilizer shock arrives as the war is recalibrating the outlook for the economy.Inflation looked tame in Wednesday's CPI report, but that was a snapshot before the war started. Since then, soaring energy prices and a recent surprisingly weak jobs report have sparked fear of an economy facing "stagflation" — sluggish growth and resurgent inflation.Food inflation would be especially visible, given the steep price increases in 2021 and 2022 that did damage President Biden's economic reputation.The bottom line: Higher prices at the pump have always been politically unpopular. Angering farmers and grocery shoppers at the same time could be especially toxic.