Nobody really knows how serious Mr. Trump was when he floated the idea of raising the gas tax in an interview with Bloomberg News. His press secretary, Sean Spicer, realizing that the president might have touched the third rail of national Republican politics, quickly tried to scale back his comment, saying Mr. Trump was not endorsing a gas tax increase but merely considering it because the trucking industry had asked him to look into it. Still, even the fact that Mr. Trump is considering an increase is encouraging.

A higher gas tax is one way to help pay for Mr. Trump’s $1 trillion infrastructure plan without increasing the federal deficit. It would benefit Americans by shortening their commutes, creating jobs and reducing costs for car repairs. Businesses would be able to ship raw materials and goods faster. All of that would bolster economic growth, which is probably why, in addition to truckers, the United States Chamber of Commerce and AAA support an increase.

Many states, tired of waiting for Washington, have raised fuel taxes. Just last month, lawmakers in California, Indiana, Montana and Tennessee voted for increases. Altogether, 21 states have done so since 2013, according to the American Road & Transportation Builders Association. But states cannot do the job alone. Many large infrastructure projects cross state lines and involve multiple modes of transportation, like road, freight rail and mass transit, putting them beyond the capacity of individual states.

Of course, there are substantial political obstacles to increasing the tax. Many conservatives, including the House speaker, Paul Ryan, and the anti-tax ideologue Grover Norquist, oppose the idea.