It was during a recent swing through Washington that Donald Trump offered a seemingly off-the-cuff idea: abolish the income tax system and make up that lost money with higher tariffs.

Economic experts quickly chimed in to question the plan's math. And on Friday, Joe Biden's White House offered a new analysis to underline why it says the idea simply won't work.

"It is mathematically unlikely that a broad tariff could ever replace the revenue raised by the individual income tax," concluded the new report from Biden's Council of Economic Advisers, the results of which were shared first exclusively with Yahoo Finance.

The report looks at imports during the 2023 fiscal year ($3.12 trillion) and found that, at a bare minimum, replacing income tax would require across-the-board tariffs of 70%. That would immediately push up prices for Americans on a wide range of consumer goods.

But it's more than that, the report finds. The issue brief contended that a range of factors — from retaliatory tariffs to decreasing demand — would lead to those higher duties generating less income for US coffers than you might expect.

"Across-the-board tariff rates would likely need to be much larger than 70 percent to raise tax revenue that is equivalent to the individual income tax," it concluded.

The new report comes as trade and tariffs remain a central issue in the 2024 campaign. "Republicans will support baseline Tariffs on foreign made goods," read the GOP platform unveiled this week. Donald Trump himself has long championed high tariffs as a way to protect the US economy and once famously called himself "Tariff Man."

Joe Biden and his campaign respond that Trump's tariff ideas are part of a larger agenda that could spur new inflation if he wins.

As recently as Thursday night at a news conference, Biden highlighted Trump's plan to impose a 10% tariff on US imports and cited a report from the left-leaning Center for American Progress, which said that the Trump idea alone "would cost the average American working family another $2,500 a year."

Why tariff returns can be diminishing

Tariffs are unpopular among many in the business community, with those duties paid by companies at US ports of entry. Historically, the costs are more or less immediately passed on to consumers buying these goods.

Also: Tariffs are also not a major income generator and currently bring in less than 2% of Federal Government receipts.

What's unclear is whether the books would ever balance if Trump won this fall — and actually tried to undertake such an effort. But the chances of his plan even happening are equally unclear: Trump hasn't repeated the idea publicly since he first floated it in June. It also didn't make the cut for inclusion on the platform unveiled this week.

As the White House report noted, a giant tariff hike would almost surely spark retaliatory tariffs from US trading partners, which would then create the need for the government to spend money to compensate affected industries. A version of this phenomenon happened during Trump's first term when retaliatory agriculture tariffs from China forced Washington to spend billions to help farmers who had suddenly lost a market for their goods.

The report also suggested that "consumption and production patterns are likely to respond" to higher tariffs. Put another way: The law of supply and demand would kick in.

What experts expect is that higher tariffs would lead to higher prices for imported goods. That would lead to less demand for them. That would lead to fewer imports and a decline in tariff revenue from what might be expected otherwise.

The White House report reflects the views of other economic experts who have looked into the topic.

Libby Cantrill is head of US public policy at PIMCO and she estimates that the Trump idea, if executed, would ultimately require tariffs north of 100%. "Trump would need Congress to eliminate the federal tax code and to impose 100%+ tariffs, and that is not going to happen," she concluded in a recent note.

A Tax Foundation analysis of the plan called Trump's plan "completely unrealistic."

Other macroeconomic effects

The White House report also sought to highlight other economic costs from Trump's plan including negative effects on economic growth and how the move would shift the tax burden onto lower-income Americans.

The report, in addition, offered a defense of Biden's own policy of targeted tariffs, calling them a tool to protect US interests while avoiding "large, negative distortions to the macroeconomy."

Biden has by and large kept Trump-era tariffs in place while adding strategically important duties on top of them. Just this week, the White House announced new measures around North American steel and aluminum markets with new actions to clamp down on tariff evasion announced in conjunction with Mexico.

In the end, the report is clearly unlikely to diminish Trump's years-long enthusiasm for tariffs. His plans for a 60% tariff on China and 10% duties on other goods remain at the center of his campaign message, where he often promises to double down on the trade policy he oversaw during his first term in office.

"China paid us hundreds of billions of dollars," Trump offered at a recent rally in Virginia of his time in office (mischaracterizing who actually pays tariff duties), but added nonetheless, "It was so because they respected our country."

Ben Werschkul is Washington correspondent for Yahoo Finance.

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