Political opportunism is pouring out of America's gas pumps, but this time it's a strange bipartisan octane.

Democratic Sen. Hillary Clinton and Republican Sen. John McCain are pushing a populist gas tax proposal that would suspend the excise tax on gasoline and diesel -- 18.4 and 24.4 cents per gallon, respectively -- for the summer months. The two presidential candidates are targeting truckers, families gearing up for the vacation season and voters desperate for relief in today's harsh economy.

The gas tax hiatus would save drivers about $2.35 per average fill-up from Memorial Day to Labor Day. For motorists who tank up once a week, that's a savings of about $35 in 15 weeks -- not much, as the other Democratic presidential candidate, Sen. Barack Obama, has correctly pointed out. Plus, there are two reasons why this modest rebate may actually hurt drivers in the long run.

First, the federal excise tax pays into the highway trust fund that helps states pay for road and bridge construction, repair and maintenance. The gas tax suspension would cost the fund about $9 billion, nearly a third of its annual revenue.

To make up for the lost dollars, Mrs. Clinton has proposed a windfall profits tax on the oil companies, which have enjoyed record earnings while Americans have suffered record prices. While the tax proposal is not a bad idea, it was raised in the Senate in March but failed to gather support. Mr. McCain would replace the highway repair money by simply shifting dollars from elsewhere in the budget.

Second, the "gas tax holiday" may not benefit consumers but instead help producers, according to the Tax Policy Center. Suspending the tax would be an incentive to purchase more gas in the traveling season that puts oil producers at capacity. Thus, with limited supply and increased demand, prices would probably rise. Drivers would lose and the oil companies would win, again.

The gas tax suspension is a shameful political stunt. Mr. McCain is using it as a wedge against the two Democratic candidates. And Mrs. Clinton is happy to set herself apart from Mr. Obama.

We urge all three candidates to focus less on short-term relief and more on long-term solutions -- like conservation, fuel efficiency, alternate sources and mass transit -- to the nation's growing vulnerability to foreign oil. The American people deserve a president who puts the public good before political gain.