President Obama on Wednesday argued that Congress must approve a temporary transportation funding bill in September, or else highway projects won’t get done, construction crews will lose their jobs, and America will fall behind in fixing its roads, tunnels, bridges and other critical infrastructure. Fox News’s headline : “Obama Calls for Extension of Gas Tax to Fund Highway Construction, Repair.” Even though the president didn’t mention the words “gas,” “gasoline” or “tax” once, and even though renewing the federal tax wasn’t a major issue any of the other times Congress recently extended the transportation bill.

Consider this a hint of what we will hear next month and beyond, when which critics will no doubt be tempted to claim that Obama and the Democrats want to “increase” your federal gas taxes merely by extending the current rate, or at the very least that the federal gas tax is another Obamaesque big-government scheme that must go. Conservative Republicans will probably have two chances to hit Obama on this — once in the debate over temporarily extending existing law to give Congress time to agree on a long-term transportation funding bill, and again when lawmakers get to hashing out the long-term policy.

Attacking America’s relatively small federal gas tax might make for great politics. But it encourages really dismal policy, subverting one of the most rational tax provisions Congress has ever managed to pass.

The original, bipartisan logic of the federal gas tax is that those who use the roads should pay for them. Taxing fuel is one way to approximate that elegant goal in the real world. Part of the reason the policy is only an approximation is that Congress didn’t index the tax for inflation, which means it has been decreasing in real dollars since the last time Congress raised it in 1993, even as the Transportation Trust Fund runs out of money. That, of course, argues for an increase.

President Obama talking about transportation funding in the White House Rose Garden on Wednesday. (LARRY DOWNING/REUTERS)

Obama, of course, won’t make this case, either. Regardless of whether Fox’s angle on the president’s Wednesday speech was misleading, the fact that he didn’t mention the gas tax is telling. Obama and his surrogates have kept miles of distance between them and proposals to raise the gas tax, particularly following an oil spike in May that the administration found politically harrowing. And the politics of tax policy have only gotten worse lately — each side claiming the other wants to raise your taxes, making the debate more about accusations than nuance.

The politics might demand cowardice on the federal gas tax. But it makes for depressing viewing. Instead of going in the right direction, the best we seem to be able to hope for is that Obama and the Democrats can keep us from hitting reverse.