The president said he struck a trade deal with Japan. Aside from his statement, the details are slim.

But it seems U.S. importers will pay a 15% tariff on Japanese goods. And the president again said that Japan will import more American goods including cars, trucks, and rice.

The Trump administration often touts his import taxes as a way to support the U.S. manufacturing sector.

The argument is: making imports more expensive incentivizes more domestic production. But the tariffs may be having the opposite effect when it comes to re-shoring manufacturing.

U.S. manufacturers already have a hard time competing with many foreign manufacturers.

“Because of the cost and availability of labor, first of all,” said Erin McLaughlin, senior economist at the Conference Board.

She said building factories and supply chains can be more expensive in the U.S. too. Then you add tariffs into the mix.

“So, any U.S. manufacturer that needs to import components from other countries will now be paying tariffs on those components,” McLaughlin said.

They may end up paying those tariffs several times.

Thomas Goldsby is a professor of supply chain management at the University of Tennessee Knoxville. He said to build a car for instance parts and sub-assemblies may go back and forth across borders.

If any step of that chain involves the U.S., “those parts could be taxed multiple times over the course of the assembly process, before ultimately being placed on a finished automobile in a U.S. production plant,” Goldsby said.

Meanwhile trade deals can give foreign companies an edge over American ones.

Teresa Fort, a professor at Dartmouth, said compare a product that’s designed by a U.S. company and made in Taiwan with one that’s designed and made in Japan.

After this week’s trade agreement, the Japanese product will have a lower tariff.

“Now with these different trade deals, there’s these examples where you’re going to perversely be taxing the foreign ideas less than the U.S. ideas,” Fort said.

All of this can mean there’s not much incentive for a manufacturer to expand in the U.S.

“It would be an incentive to expand production elsewhere,” said Kadee Russ, an economics professor at UC Davis. “Where they don’t face tariffs on imported inputs.”

A recent paper written by researchers at the Federal Reserve Board of Governors found that the tariffs imposed during the first Trump administration caused producer prices to rise, and manufacturing employment to fall.