Donald Trump on Friday plans to carry our his threat to slap tariffs on foreign steel and aluminum in an effort to protect American jobs and steel producers, but like many presidents before him, he probably won’t have much success.

The Trump administration on Thursday indicated the tariffs will go into effect within 24 hours, a move that reflects the White House’s inability to strike deals with its closest trading partners to avert such a showdown.

Also Read: Here’s what businesses did with Trump tax-cut windfall. Hint: they didn’t spend it

Trump joins a long list of presidents going back to Richard Nixon who’ve sought to use tariffs and other restrictions to protect a long-ailing U.S. steel industry whose heyday ended decades ago. Trump campaigned in 2016 against what he called “unfair trade” and promised to get tough with trading partners.

The decision saddled an already jittery Wall Street with fresh worries. Other nations have promised to retaliate, raising the odds of a trade war that could harm the economies of all involved. U.S. stocks DJIA, -2.60% SPX, -1.89% fell sharply on Thursday and the 10-year Treasury TMUBMUSD10Y, 0.662% note fell a few basis points to 2.83%.

The White House said the tariffs are needed to ensure a domestic supply of a material vital to national defense, but the real goal is to protect American workers from cheap foreign steel it claims is unfairly subsidized. A Commerce Department report pointed to several mill closures in the past few years and the loss of several thousand jobs.

Also Read: Upbeat ‘Beige Book’ prognosis of economy keeps Fed on track for June rate hike

The U.S. already imports four times as much steel as it exports, and imports are on the rise again. While the U.S. imports steel from more than 100 countries, three-quarters come from just eight countries, according to the International Trade Organization.

The top supplier to the U.S. in 2017 was Canada, followed by Brazil, South Korea, Mexico and Russia. Other notables include Turkey, Japan and Taiwan.

China is just outside the list at No. 11 despite producing about half of the world’s steel. Barack Obama is the only recent president not to impose broad tariffs, but he did put significant restrictions on Chinese steel.

Steel has long been a politically sensitive issue, especially since much of the production takes place in swing states such as Pennsylvania. Pro-union Democrats have pushed for tariffs and other restrictions for years — many quietly support Trump’s move — and it’s one of the few industries that Republican presidents have singled out for protection.

The decline in U.S. steel jobs, however, has been going on a long time despite frequent interventions by Washington.

Also Read: Consumer spending surges for second straight month. Inflation, not so much

Steel now directly employs about 140,000 workers, according to Bureau of Labor Statistics. More than half a century ago as many as 650,000 people were employed in the industry.

The steel industry has undergone vast changes since the end of World War Two. For one thing, a stream of technological advances have spawned huge increases in productivity, allowing steelmakers to do more with fewer workers.

Steelmakers also gather up and reform scrap metal more than ever, a form of recycling that also requires fewer workers.

Stiffer foreign competition and more imports, to be sure, have contributed to the loss of American steel jobs. Just how much has been hotly debated for years, but research suggests it’s played a smaller role.

In any case, the penalties probably won’t achieve their intended affect. Tariffs imposed by prior presidents from both parties, including George W. Bush, Bill Clinton and Ronald Reagan, have done little to stem the tide.

The last major round of steel tariffs, imposed by Bush in 2002, did more harm than good to the U.S. economy, several studies later concluded.

Higher tariffs have encouraged other U.S. manufacturers to seek out cheaper substitute materials to avoid the higher cost of steel that often results.Or they’ve tried to pass the cost onto customers. And in the worst-case scenario they’ve had to reduce production or layoff workers to cope with higher steel prices.

Most American businesses aside from the steel industry oppose the new tariffs.

The U.S. Chamber of Commerce, for example, warned tariffs could do enough harm to “put at risk the economic momentum achieved through the administration’s tax and regulatory reforms.” The group urged the White House not to proceed, saying the tariffs would damage the economy, harm relationships with longstanding partners and undermine U.S. leadership.

Commerce Secretary Wilbur Ross dismissed those worries, saying all the countries involved “will get over it in due time” after a compromise is eventually reached.