How did a simple, logical and once-bipartisan policy such as the gas tax become such a political land mine that neither Democratic nor Republican presidents will touch it? The federal taxes on gasoline and diesel fuel haven't been increased in nearly 30 years, leaving less money over time to pay for roads, bridges and public transit improvements. But even a modest proposal to raise the tax by a few cents per gallon to help fund infrastructure investments has been batted down by President Biden. White House Press Secretary Jen Psaki called the gas tax hike a "nonstarter" this week because it would violate Biden's pledge not to raise taxes on Americans making less than $400,000 a year. Democratic senators have dismissed the proposal to raise the gas tax as a "Republican thing." These are the same leaders who have — rightly — vowed to fight climate change on every front. So why are they refusing to even consider raising the price of the fossil fuels that power cars and trucks? The transportation sector is the biggest source of greenhouse gas emissions in the United States. Political leaders' obsession with maintaining cheap gas undermines efforts to get people into cleaner, more fuel-efficient vehicles and to cut emissions from transportation. A gas tax increase should be considered an essential piece of any infrastructure package. It's true that any fuel tax hike that's small enough to be politically feasible would raise far less than the $2 trillion needed to finance Biden's initial proposal or even the $1 trillion required for the scaled-back version being negotiated by Democrats and Republicans in Congress. Both proposals would stretch over eight years. By contrast, raising the tax 15 cents per gallon and pegging future increases to inflation would generate about $200 billion over the same period. Still, the higher gas tax revenue could be an important piece of the funding puzzle, along with raising taxes on corporations and high-income households, as the Biden administration has proposed, or repurposing uncommitted COVID-19 relief dollars, as Republicans have suggested. More important, though, increasing the gas tax would restore a consistent source of transportation funding that has been depleted over time. Created in 1956, the federal Highway Trust Fund was envisioned as a user-supported system, with drivers paying taxes at the fuel pump to finance roads, highways and bridges. For decades there was bipartisan support for raising the gas tax when needed to keep up with inflation and demand.