President Trump says planned tariffs on Canada and Mexico will go into effect on Tuesday because too much fentanyl is pouring across U.S. borders.

Mr. Trump announced the plan on Thursday, ending days of confusion about whether the 25% levies would happen or be delayed a second time.

“More than 100,000 people died last year due to the distribution of these dangerous and highly addictive POISONS,” Mr. Trump posted on Truth Social. “We cannot allow this scourge to continue to harm the USA, and therefore, until it stops, or is seriously limited, the proposed TARIFFS scheduled to go into effect on MARCH FOURTH will, indeed, go into effect, as scheduled.”

The president said that his new 10% tariff on China will be implemented Tuesday and that reciprocal tariffs on a range of nations will go into effect on April 2.

Wall Street reacted negatively to the news, with Dow Jones Industrial Average futures turning negative after the president’s post.

Tariffs are a tax or duty paid by importers on the goods they bring in from foreign markets.

Mr. Trump says tariffs are a great way to force companies to return to America or keep their operations in the U.S., employ American workers and create revenue to fund domestic programs.

Presidents can impose tariffs without Congress in certain situations, such as to protect national security or address international emergencies.

The U.S. relied on tariffs as a primary source of government revenue until the federal income tax was imposed in the early 20th century.

But tariffs can also result in higher prices for consumers.

Foreign countries don’t pay the tariffs directly to the U.S. Treasury. In many cases, U.S. companies will pay the levies, and they might pass on at least some of the cost to consumers through higher prices.

Business lobbies have objected to the tariffs, citing increased costs along the supply chain.

The automobile industry says the tariffs will be a destabilizing force, given the interconnected nature of the sector among Mexico, U.S. and Canada.

Tariffs could also impact the price of avocados, tomatoes, berries and other produce from south of the border.

Democrats say Mr. Trump’s tariffs amount to a tax on everyday consumers and flies in the face of Mr. Trump’s campaign pledge to rein in costs.

They say there are better ways to deal with fentanyl — such as treatment and screening at ports — than imposing tariffs on friendly neighbors.

Chinese manufacturers make precursor chemicals for fentanyl that reach Mexico, where cartels finish the drug product and send it into U.S. communities. A tiny percentage is seized at the Canadian border.

The Centers for Disease Control and Prevention reports provisional data on overdose deaths each month, though the figures lag by nearly half a year.

The rate of U.S. overdose deaths steadily climbed during the COVID-19 pandemic that spanned the last year of the Trump administration and the first years of former President Joseph R. Biden’s term — often topping 100,000 on an annual basis — before turning sharply downward in 2024.

More than 84,000 people died from U.S. overdoses during the 12 months that ended in September, the most recent yearlong stretch available.

• Tom Howell Jr. can be reached at thowell@washingtontimes.com.