President Donald Trump’s plan to revitalize America’s old, deteriorating infrastructure has two major problems. First, it doesn’t promise enough money. According to the American Society of Civil Engineers, the U.S. needs a $2 trillion investment in its roads, bridges, water, and sewage systems in order to become globally competitive. Trump’s proposal, unveiled on Monday, only calls for three-quarters that amount.

Second, only $200 billion of his $1.5 trillion plan is a guaranteed investment from the federal government. The rest is supposed to come from state and local governments and private companies, which theoretically would be incentivized to spend money on projects through grants, loans, or lines of credit from the federal government. It’s a risky bet that $200 billion of federal money will create $1.3 billion in investment from other entities. Analysts tell CNN it’s possible, but far from certain.

But there’s a solution to both of these problems: Raise the gas tax.

The federal tax on gasoline has stood at 18.4 cents per gallon for the last 25 years, never budging even for inflation. Phasing in a 25-cent increase over five years and indexing the tax to inflation would generate nearly $400 billion over a decade, according to the U.S. Chamber of Commerce, which is calling for a raise.

The powerful business lobby’s support is notable, since new taxes are a non-starter for most Republicans. But lately, some conservative Republicans in Congress are warming to the idea. Trump seems to like the idea of raising the gas tax, too. In May, he said he was open to the idea if the money went toward highway projects. And last month, he “privately suggested massively increasing the gas tax to help fund national infrastructure overhaul,” The Washington Post reported, adding that Republican leaders in Congress “moved quickly to shut down the idea.”

But this is the rare Trump idea that makes policy sense. America’s roads, highways, and bridges are in disrepair, and those who rely on them deserve a guaranteed source of revenue to fix them. As Trump faces questions about the funding mechanism for his infrastructure overhaul, the question is whether he and congressional Republicans will do what’s fiscally prudent, or cave to the billionaire fossil-fuel interests that hold such sway over the party.

Today, the federal government taxes gasoline in order to make drivers pay for maintaining the roads and bridges they use, as well as public transportation projects. But it was not always this way: The first gas tax was signed into law as a way to reduce the federal deficit during the Great Depression. It was signed into law by President Herbert Hoover in 1932 at one cent per gallon.

The gas tax steadily rose, but changed significantly in 1983, when President Ronald Reagan signed a law that more than doubled the tax from 4 cents to 9 cents and distributed the revenue to the highway trust. It was another Republican president, George H. W. Bush, who increased the rate next, by 5 cents in 1990. Bill Clinton was the final president to raise the gas tax, by 4.3 cents in 1993.

The 18.4-cent gas tax may have been adequate in 1993, but it’s not anymore. According to the Pew Charitable Trust, revenue from the gas tax “buys nearly 40 percent less than it did” in 1993 when the price was set. At the same time, both the cost and number of necessary projects are rising. Transportation Secretary Elaine Chao has said the trust fund spends $10 billion more than it collects every year. It is in danger of running out of money. There are 56,000 structurally deficient bridges across the country today, and one in five miles of highway is in poor condition.

The public supports raising the gas tax—albeit barely, and only if the money is used to fund infrastructure improvements. The most recent national poll, released in July by Bloomberg, found 55 percent of Americans in favor. But there wasn’t equal agreement across the aisle: 67 percent of Democrats favored raising the tax, versus only 51 percent of Republicans.

That’s one reason congressional Republicans would be hesitant to support a raise. Another is historical: As Alec MacGillis explained for ProPublica in 2015, Democrats raised the tax in 1993 under President Bill Clinton and then were annihilated in the midterm election of 1994. This impressed on the George W. Bush administration that “a gas tax increase was not to be discussed,” MacGallis wrote. And then there’s the fact that conservative groups connected to the billionaire Koch brothers are among the most outspoken opponents of a gas tax hike. Most Republicans up for re-election in 2018 will avoid crossing the Kochs at all costs.

The Kochs owe their wealth to fossil fuels—Koch Industries began as an oil refinement company—so they’re opposed to anything that might encourage Americans to drive less. A 25-cent-per-gallon hike, they argue, “would lead households to spend an additional $285 on gas on average annually.” Gas is undoubtedly expensive, but that’s not because of the gas tax, which has remained the same for 25 years. In fact, because of improved fuel efficiency, the average person uses less gas than they once did to travel the same number of miles. This is great for people’s wallets—not to mention for the environment and public health—but it’s bad for roads and bridges, because less money goes into the federal trust fund for infrastructure improvements.

Rather than raise the gas tax to correct for fuel efficiency, though, Trump is pushing reforms that would make vehicles less fuel efficient. Last year, he ordered a review of the Obama administration’s Corporate Average Fuel Economy standards—or CAFE Standards—which require the American fleet to improve its average fuel usage from 35.5 miles per gallon to 51.4 miles per gallon by 2025. Meeting those standards would require an increase in more efficient gas-powered cars, and far more electric cars on the road. The results of Trump’s review are pending, but Bloomberg reported that his administration is considering requiring a 35.7 miles per gallon average by 2026—a dismal .2 miles per gallon increase in fuel efficiency.

If Trump makes cars less efficient, while maintaining the 1993 gas tax, he would inadvertently raise more money for federal infrastructure: Consumers would have to buy more gas to travel the same distance, so revenue from the gas tax would increase. But the cost to consumers would be similar if Trump just maintained strong fuel efficiency standards and raised the gas tax. The only difference is that Trump’s scenario forgoes the public health, environmental, and climate benefits that come from using less fossil fuels.

And there’s the issue of electric cars, which raise zero dollars for the infrastructure fund. The industry-funded Institute for Energy Research, founded by Charles Koch and run by a former Koch lobbyist, warns that “if electric vehicles were to represent 60 percent of U.S. new car sales by 2030, annual tax revenue (federal and state) would be reduced by $10 billion, or about 14 percent compared to if electric vehicle sales remained flat at 1 percent of new car sales.” But that can be solved simply by instituting a uniform fee on electric car sales, as seventeen states have done. Slate’s Daniel Gross once slammed this idea as “punishing” people for buying hybrid and electric cars, but that’s not the case—it just levels the playing field. Everyone who uses the road should pay for its upkeep.

In a perfect world, we wouldn’t have a gas tax or an electric car fee, because both are fundamentally unfair policies. Under a gas tax, poor people are made to spend more on gas because they have cheaper, less efficient cars. With an electric car fee, as Gross points out, “you get taxed just for owning the car, not whether you drive it or not.” Instead, people should be taxed for the number of miles they drive. But it would take years for such a novel idea to gain enough supporters in Congress, not to mention the public at large. Americans who commute on crumbling roads and bridges every day can’t wait that long. Today’s political environment offers the chance, however slim, to raise the gas tax. If only Trump and congressional Republicans were bold enough to take it.