Trump’s signature economic policy achievement from his first term is due to expire at the end of this year, but he and top Senate Republicans have called for making it permanent.

Some fiscal conservatives have pushed back, however, leading a Republican lawmaker to ask CBO for an estimate on what that would do to the national debt.

In response, CBO said Friday that if the Tax Cuts and Jobs Act was extended permanently and there were no other changes to fiscal policy, debt held by the public would reach 214% of GDP in 2054.

And assuming borrowing costs face more upward pressure amid the deteriorating fiscal situation, amounting to an additional 1 percentage point, debt would hit 204% of GDP in 2047 and exceed 250% in 2054.

Total US debt is $36 trillion, and debt held by the public is about $29 trillion. The cost to service US debt payments already tops $1 trillion a year, even more than the Pentagon’s budget, adding further to the debt.

“Macroeconomic feedback effects would further increase interest rates and, therefore, lead to even worse fiscal outcomes,” the Peter G. Peterson Foundation warned. “Such findings demonstrate the sensitivity of the nation’s finances to borrowing costs.”

Under CBO’s current baseline estimate that assumes the tax cuts expire—an unlikely scenario—US debt would climb to 166% by 2054 from 99% today. Even that forecast would break records, topping the previous high during the immediate aftermath of World War II, while debt would also continue rising.

A White House official told Fortune that the Trump administration’s supply-side reforms, such as more energy production, deregulation and spending cuts, will spur growth and expand the tax base. That would also lower inflation, allowing the Federal Reserve to cut interest rates and ease borrowing costs.

The official added that the administration plans to raise revenue from tariffs, noting that Trump’s China duties from the first term raised hundreds of billions of dollars without having much impact on inflation or growth.

The CBO report did not gauge how sustainable the projected debt would be. But if it exceeds 200% of GDP, it would violate a maximum level outlined by the Penn Wharton Budget Model.

In an October 2023 report titled “When Does Federal Debt Reach Unsustainable Levels?,” it said US debt held by the public cannot exceed 200% of GDP, even under the favorable market conditions at that time.

While Japan has an even bigger debt burden, it’s not a relevant example because its higher domestic savings rate allows the country to absorb more government debt.

“This 200 percent value is computed as an outer bound using various favorable assumptions: a more plausible value is closer to 175 percent, and, even then, it assumes that financial markets believe that the government will eventually implement an efficient closure rule,” the report said. “Once financial markets believe otherwise, financial markets can unravel at smaller debt-GDP ratios.”

The CBO’s estimate comes as debt warnings have been piling up. Most recently, billionaire investor Ray Dalio predicted the US is headed for an imminent debt crisis.

Eventually, the supply of debt that the US must sell will be greater than demand in global financial markets, leading to “shocking developments,” he warned at the CONVERGE LIVE conference in Singapore earlier this month.

“There may be restructurings of debt, there may be exerting pressures on countries to buy the debt, to own the debt, political pressures on countries,” Dalio said. “There may be cutting the payments to some predator countries off for political reasons, there may be monetizations of debt.”