Well, it would seem that he wants to use the part of the Federal Gas Tax that funds roads and bridges for the tax holiday. So maybe he's only holidaying part of it.
YES, YES, YES... I'LL HELP YOU WITH GAS PRICES; I'LL HAVE A FEDERAL GAS TAX HOLIDAY FOR THREE MONTHS. THAT WILL SAVE YOU 18 CENTS PER GALLON! WHICH WILL BE WORTH NOTHING IN ABOUT 12 DAYS DUE TO INCREASING GAS PRICES.
