Donald Trump made major new promises on tariffs last week — the latest in a series of over-the-top promises to use them to benefit the United States.

On his social media platforms, he declared that he wanted to create what he called an "Internal Revenue Service" to collect duties and other revenue from foreign sources.

To be clear, the name itself is misleading: the vast majority of tariffs are American Businesses import goods rather than through external foreign sources.

The article is the latest in a series of pledges Trump has made on tariffs, which are central to his economic strategy. Economists say these tariff commitments will be difficult to keep and some will even offset each other.

Targets of tariffs: Revenues, jobs and the war on drugs

One of Trump's big tariff promises is to raise revenue. During the campaign, he tell the crowd in georgia "We will inject hundreds of billions of dollars into our national coffers and use them to benefit American citizens."

He has also repeatedly said that tariffs will boost U.S. manufacturing. In the same speech in Georgia, Trump said he would impose tariffs on cars made in Mexico. "We're going to put a 100 percent tariff on every car that comes across the Mexican border and tell them the only way they're going to get rid of the tariffs is if they want to build a factory in the United States and have you run that plant."

in a Recent press conferencesHe also said tariffs could deter illegal immigration and drugs.

"Mexico must stop allowing millions of people to pour into our country," he said. "We're going to have very tough tariffs on Mexico and Canada because Canada, they're also passing through Canada, and there's record amounts of drugs coming through Canada."

These tariff targets are conflicting

Sounds great—a simple trick for solving drug, debt, and employment problems. But it’s hard to see how this could all happen at the same time.

“You can impose tariffs on income or you can impose tariffs on restrictions, but you can’t do both,” said Erica York, vice president of federal tax policy at the Tax Foundation, a right-leaning economic think tank.

Since tariffs are taxes that U.S. importers pay on goods from other countries, tariffs do generate some revenue.

But Trump also hopes to use tariffs to boost manufacturing. The idea here is to make foreign cars more expensive, which means Americans will buy fewer foreign cars.

Herein lies the great paradox: If Americans buy fewer foreign cars, tariff revenue will fall.

That’s not the only contradiction York sees in Trump’s policies. If Trump threatens to impose tariffs on Mexico or Canada and succeeds in getting them to crack down on immigration or drugs — that is, if Mexico or Canada changes their policies to remove Trump from office no Put tariffs on them — which means no additional revenue and no additional protections for American workers.

"The way the incoming Trump administration talks about this is that they can have their cake and eat it too. But that's not the case," York said.

NPR asked the Trump team to explain how tariffs could achieve all of Trump's stated goals. They did not answer specifically, but said the tariffs would "protect American manufacturers and workers from unfair practices by foreign companies and foreign markets."

Price increases and income uncertainty

Trump’s tariff proposals go far beyond those enacted during his first term. He has imposed tariffs of up to 60% on Chinese goods and proposed 25% tariffs on Canada and Mexico. He even suggested imposing tariffs of 10% to 20% on all imported products.

But even high new tariffs won’t raise the revenue Trump seems to want. Trump often points to the 19th century, the era before the federal income tax, as an era he admires.

"This will make our country rich," he told a conference. December press conferencespoke with admiration of the days of former President William McKinley. "That's when we were proportionately the richest," Trump said.

During the campaign, Trump even hinted that he wanted to replace income taxes with tariffs.

Experts say this is impossible. Last year, tariffs accounted for only 2% of government revenue.

according to an analysis Data from the Peterson Institute for International Economics shows that the maximum revenue that Trump's threatened tariffs could generate would be $780 billion. That’s about a third of total income and corporate tax revenue, and that doesn’t take into account the economic impact of higher tariffs, such as higher prices and slower growth, not to mention retaliation from foreign countries.

Kimberly Clausing co-authored the analysis and also worked in the Biden Treasury Department. She stressed that higher tariffs would hurt lower-income Americans the most through higher prices while helping higher-income people accept Trump's proposed tax cuts.

"I think a cynical reading of the Trump administration's proposals is that a series of regressive tax cuts are intended to help those at the top of the distribution, and those tax cuts are paid for through regressive consumption taxes, And this will hit the poor hardest," she said.