Trump wants a gas tax holiday. There's a much bigger problem looming

An American flag flies above a sign displaying gas prices at a gas station in Arcadia, Calif., on May 11. Mario Tama/Getty Images hide caption toggle caption Mario Tama/Getty Images Stay up to date with our Up First newsletter, sent every weekday morning. President Trump has called for a temporary waiver of the federal gas tax, which costs drivers 18.4 cents per gallon. It's one of several attempts to relieve pain at the pump as voters grow increasingly frustrated with gasoline prices, which have hit four-year highs thanks to the oil trade disruption triggered by the war with Iran. A national gas tax holiday would require an act of Congress. Lawmakers have floated the idea, with several bills introduced before Trump called for a temporary pause on the tax. But even with the president's backing, it's not clear whether his proposal will make it to the floor for a vote. Gas tax holidays are controversial, with advocates arguing they provide quick relief and with critics denouncing them as costly and even counterproductive. Here's what you need to know. How much would a federal gas tax holiday save? At most, waiving the tax would save drivers 18.4 cents per gallon, or $2.76 on a 15-gallon fill-up. The national average price for a gallon of gasoline is now $4.46, up from around $3 prewar, so the relief would make up for only a fraction of that price spike. But there are two reasons that drivers might save even less. …