President Donald Trump demands that gasoline retailers immediately lower pump prices to about $2.50 per gallon after crude oil falls to roughly $68 per barrel, warning of "big problems" for sellers that do not comply.He directs the Department of Justice to investigate gasoline price gouging, accuses some retailers of overcharging, and singles out California for high fuel taxes while economists say retail prices lag due to refining, transportation, seasonal blends and previous higher-cost purchases.The national average for gasoline is about $3.92 per gallon with several regions above $5.00, and Trump frames his demand as a way to lower inflation and household costs while Republicans face pressure ahead of elections.