Trump’s tariffs are a “dirty tax” that will worsen the $38.6 trillion national debt crisis in the long term, a top analyst says.

Kent Smettes, faculty director of the Penn Wharton Budget Model, challenges the narrative that tariffs are a tool to protect domestic industry. In a recent interview with wealth, Smettes backed what he said was his long-standing view that large-scale tariffs are a “dirty VAT” (value-added tax) — a policy he believes is far more damaging to the U.S. economy than traditional tax increases.

While economists generally view a flat, broad-based VAT as an effective method of raising government revenue, Smettes distinguishes tariffs as a “dirty” variation because they are much less uniform. A standard VAT is widely applied, distorting decisions primarily between spending now and saving for later. However, tariffs target specific goods, causing consumers and businesses to change behavior in inefficient ways to avoid the tax.

What’s more, Smettes said, despite the tariffs being presented as a deficit-reduction tool that will bring in revenue that will make a significant difference to the United States’ $38.6 trillion national debt, he sees things differently.

“We have a lot of debt and we will pay down more and more debt along our current baseline,” Smettes said, adding that he sees a future where investors demand higher returns to keep investing in the U.S. and a “feedback effect” that will continue to increase debt well into the future.

The Supreme Court has weighed in on the legality of many of Trump’s tariffs since hearing arguments in November, with several Trump-appointed justices taking a stand on the matter. Their decision can be made as soon as Friday.

A central flaw in the tariff strategy, according to Smettes, is a misunderstanding of what America actually imports. He notes that 40 percent of imports are not final goods destined for store shelves, but intermediate inputs used by American companies to manufacture their own products. As a result, the tariffs act as a tax on American producers, raising their costs and making them less competitive globally.

“The idea that this is pro-American is actually the exact opposite,” Smettes said. “It Hurts American Manufacturers.” He cited the example of companies like Deere, arguing that the US economy benefits when such firms focus on high-margin intellectual property rather than making low-margin components such as screws or steel strip. By taxing these inputs, the policy effectively penalizes domestic production.

Deere has repeatedly quantified tariffs as a major cost element, disclosing costs of about half a billion dollars for the full 2025 fiscal year and projecting a $1.2 billion hit for 2026. Management described the tariffs (on metals and certain imported components) as causing “margin pressures” and weaker operating profits, even as operating income held up. According to Smetters, Deere has been evaluating and renegotiating supply contracts and considering shifting some sourcing and manufacturing footprints to reduce exposure to tariffs and input cost increases.

Americans shouldn’t want Deere to supply them with steel and bolts, he argued.

“It’s very low-margin stuff,” he said. “We want them to focus on high-margin intellectual property, which they do.” He added that he believed this was “really missing” from the wider discourse.

Smetters shared projections from the Penn Wharton budget model that show that while the immediate impact of the tariffs may seem manageable — potentially cutting GDP by just 0.1 percent in the first year — the long-term outlook is bleak. Smettes projected a reduction in GDP of about 2.5% over 30 years, given the debt impact this dirty tax would add by escalating debt interest payments.

The main driver of this decline is this “massive feedback effect” on US debt. As U.S. companies become less efficient and the government floats more debt, Smettes explained that global investors will demand a higher return (or risk premium) for holding U.S. Treasuries. In this sense, the tariff problem is really a national debt problem.

“Think about US Treasuries,” he said, predicting that US investors will demand a higher return on investment. “What if the private market now has to pay a higher profit to attract investment because it has higher costs?”

The only result, he said, is that the Treasury will pay a higher return to investors over an increasingly long time. The U.S. is at real risk of turning into Japan — a favorite doomsday prediction of macro analysts such as Societe Generale’s Albert Edwards — which has been paying out more than 25 percent of its income in interest payments since its stock market bubble popped in the early 1990s. The U.S. is set to pay $1 trillion in interest payments next year, he said, “and climbing.”

To illustrate the inefficiency of tariffs, Smettes compared them to a hypothetical increase in the corporate tax, which is usually considered the least effective way to raise revenue. He estimates that to raise the same amount of revenue as the proposed tariffs, the US would have to raise the corporate tax rate from 21% to 29%. However, the economic damage from the tariffs would be “2.5 times worse” than that corporate tax increase.

Smettes clarified that he’s not in favor of raising corporate income tax revenue — he’s not advocating for any policy in particular — but he’s essentially surprised that Trump has found a new form of the most ineffective tax increase possible: “Well, Trump just found a new one. It’s even more ineffective than that.”

Smettes noted that a “destination-based” tax proposed in 2016 could have achieved similar revenue goals more effectively. However, this proposal was effectively shot down by major retailers, including Walmart, who feared it would increase their import costs. Instead, the U.S. is left with what Smettes calls a “dirty” alternative — a sales tax disguised as trade policy that risks stifling the very growth it promises to protect.

This story was originally featured on Fortune.com

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