The stock market is struggling to adapt to President Trump’s aggressive tariffs. Economists are downgrading their growth forecasts. Some are predicting a recession. Voters are souring on Trump’s handling of the economy, just two months into his second presidential term.

With all the churn, it’s worth asking: What is this all about, anyway? Why is Trump doing this? Is it worth the trouble?

Read more: What Trump’s tariffs mean for the economy and your wallet

Trump has offered a variety of rationales for the tariffs he has imposed on… well, the latest count is thousands of imported products from dozens of countries. Trump wants trade partners to help stem the flow of migrants and fentanyl into the United States. He wants more federal revenue from tariffs. He wants to punish nations that have put more limits on buying US products than the United States has put on theirs.

But there’s one overriding Trump aim: to beef up domestic manufacturing and add more blue-collar jobs. “We’ll impose new tariffs so that the products on our stores will once again be stamped with those beautiful words, made in the USA,” Trump said in a January speech previewing his second term. He highlighted more domestic production of cars, lumber, ships, and many other things as hallmarks of his new “golden age” in America.

Manufacturing is important, but it’s not where you’d likely start in a clean-sheet effort to turbocharge the US economy. Manufacturing accounts for just 10% of GDP, a portion that has gradually declined since the 1980s. We still build a lot of stuff in America. Industrial output is close to record highs. But manufacturing requires fewer and fewer workers, for obvious reasons.

Producers continually adopt automation and manufacturing gets more efficient. It is true that some manufacturing capacity has left the United States for overseas markets, contributing to the loss of blue-collar jobs. But if that work had stayed, the same efficiency forces would have applied and the nation would have continued to make more stuff with fewer workers.

This trend is very familiar. Agriculture used to employ a majority of Americans, but the industrialization of the economy in the 1800s and 1900s changed that. The farm economy today accounts for just 1.2% of all jobs. And thanks to massive efficiency gains, those workers provide plenty of food for the US market, as well as for export.

Trump’s tariff plan is basically an effort to push the US economy back in time, like somebody in the middle of the Industrial Revolution agitating to keep all the workers on farms. “The problem is that it isn’t the 1950s or 1960s anymore,” Douglas Holtz-Eakin, former director of the Congressional Budget Office and head of the American Action Forum think tank, explained in a recent blog post. “Manufacturing jobs have been declining for generations from a complex set of forces that cannot be offset by a simplistic reliance on tariffs. There are no jobs to ‘bring back.’”