U.S. average gas prices have hit $4 per gallon nationwide, per AAA.Why it matters: It's a 35% increase at the pump since the war in Iran began last month, and there's little hope that costs will ease as the Strait of Hormuz remains closed to most ships, straining supplies worldwide.Approximately 20% of the world's oil supply travels through the Strait.Driving the news: Oil prices have surged to over $100 a barrel or more since the war began, raising the prices that consumers pay when they fill up.A month ago, regular gas averaged $2.98. A year ago, it was $3.17. Zoom in: The national average now rests at $4.018 for regular gas, $4.541 for mid-grade, $4.904 for premium, and $5.454 for diesel.Flashback: Gas prices last averaged $4 per gallon in 2022 after Russia invaded Ukraine.The U.S. is still far off its highest average gas price of $5.03 a gallon in June 2022.By the numbers: 48% of Americans blame President Trump and his administration for the gas price surge, per a Morning Consult poll earlier this month.16% blamed oil and gas companies, 13% blamed global market forces, and 11% blamed former President Biden.87% of those polled by Reuters/Ipsos say they expect gas prices to increase as the war drags on, and 55% said that rising pump costs have "somewhat" impacted their overall household budget.Go deeper: Trump faces limited gas-price options on Iran