John McCain recently proposed a “gas tax holiday” - a suspension of the 18.4-cents-per-gallon gas tax during the summer, which is peak driving season. Hillary Clinton has also supported this plan to ease the pain of skyrocketing gas prices. Now economists - and Barack Obama - are saying it’s a bad idea.

Here’s what Princeton economics professor and New York Times columnist Paul Krugman has to say about it:

Why doesn’t cutting the gas tax this summer make sense? It’s Econ 101 tax incidence theory: if the supply of a good is more or less unresponsive to the price, the price to consumers will always rise until the quantity demanded falls to match the quantity supplied. Cut taxes, and all that happens is that the pretax price rises by the same amount. The McCain gas tax plan is a giveaway to oil companies, disguised as a gift to consumers.

Is the supply of gasoline really fixed? For this coming summer, it is. Refineries normally run flat out in the summer, the season of peak driving. Any elasticity in the supply comes earlier in the year, when refiners decide how much to put in inventories. The McCain/Clinton gas tax proposal comes too late for that. So it’s Econ 101: the tax cut really goes to the oil companies.

A-ha. Of course the gas tax holiday was too good to be true - and didn’t it sound nice? Everybody loves a holiday. I’m no math major, but I’ve dabbled in Econ and Krugman’s explanation makes complete sense.

Clinton has been “commuting” around Indiana to win votes, and Wednesday morning she “rode to work” with a sheet metal worker and stopped at a gas station to show that she knows how much blue-collar voters are struggling with high prices. ABC News paints an amusing picture of her “commute”:

Wilfing picked up Clinton from her hotel in the boss’s truck for arguably one of the nation’s most unusual midweek commutes. Trailed by several police cars and surrounded by two rather large suburbans, Wilfing drove with Clinton in the passenger’s seat and an armed Secret Service agent keeping watch in the back.

Meanwhile, Clinton’s still accusing Obama of being “out of touch” with voters struggling with high gas prices, as he opposes the gas tax holiday. He says, as many economists do, that the only way to lower gas prices is to use less oil, and that high prices are better for the environment because they encourage (force?) drivers to seek less costly and more earth-friendly modes of transportation. Obama is seizing the opportunity to slam Clinton’s position on the gas tax holiday - a potential benefit for him in the upcoming Indiana and North Carolina primaries:

“It would last for three months and it would save you on average half a tank of gas, $25 to $30. That’s what Senator Clinton and Senator McCain are proposing to deal with the gas crisis,” he said on Tuesday in Winston-Salem, North Carolina.

“This isn’t an idea designed to get you through the summer, it’s an idea designed to get them through an election.”