President-elect Donald Trump’s pledge to enact sweeping tariffs is one of the most important and controversial aspects of his economic plan for a second term. After the already sizable tariffs he imposed during his first presidency, he has said he would slap new levies of 10% to 20% on every U.S. trading partner, 60% on goods from China, and as much as 1,000% in other circumstances.

Most economists are deeply opposed to Trump’s proposals, which they say will drive up prices for U.S. consumers. But throughout American history, the calculus for tariffs has always been far more complicated than their effect on consumer prices — and even that is not as perfectly understood as economists sometimes pretend it is. Nor is the long-standing conceit that free trade is a win-win actually true.

That helps explain why the Biden administration also embraced tariffs. Not only did President Joe Biden not roll back Trump’s original tariffs, but he ordered new ones on Chinese imports both high tech — electric vehicles, semiconductors — and low tech, like syringes. Biden’s tariffs are far different from Trump’s, but they are tariffs.

The embrace of tariffs is a massive change historically. “There was a generalized push for liberalizing trade,” says Jason Furman, a former chairman of the Council of Economic Advisers who is a professor at Harvard University. “Today, the push for liberalizing trade is gone and the protectionism has gone up.” Why has this happened — and if tariffs aren’t actually all bad, is there such a thing as balance?

The obvious reason that politicians have embraced tariffs is the most cynical one. Tariffs, whatever repercussions they might have economically, are politically popular. More than half of registered voters said they would be more likely to back a candidate who supported imposing both a 10% tariff on all imports and a 60% tariff on imports from China, according to a Reuters-Ipsos poll in September.

Maybe voters innately understand that tariffs are about more than consumer prices, which is why they have a long, contentious history in American life. Early politicians, most prominently Alexander Hamilton, supported their use to build nascent American industries. Others, like his rival Thomas Jefferson, disagreed vehemently. The century-plus of back and forth came to an end — sort of — after 1930, when the Hoover administration, over the objections of economists, passed the Smoot-Hawley Tariff Act, which is widely believed to have exacerbated the Great Depression, and killed off any lingering belief that broad-based tariffs were a cure-all. (Until Trump.)

While politicians continued to flirt with tariffs — for instance, despite all his talk of the beauty of free trade, President Ronald Reagan imposed onerous tariffs on Japan — overall, there was a growing embrace of free trade. But the embrace was never based purely on economics. In 1948, Paul Samuelson, winner of the Nobel Prize in economics, argued aggressively for free trade, in part because, he wrote, for the United States to do otherwise would be to “attempt to snatch prosperity for ourselves at the expense of the rest of the world,” as Oren Cass, founder of American Compass, has noted. Foreign Policy wrote that President John F. Kennedy pushed the Trade Expansion Act of 1962 through Congress in part to contain the threat of competition from the Soviet Union. During those years, of course, the United States could afford to be beneficent.

Even though the case for free trade wasn’t always made on the basis of the numbers alone, the economic ideology that free trade was good hardened into something approaching a religion. It was supposed to benefit everyone, including workers. Job losses were supposed to be mainly the result of technological changes, not competition from foreign goods.

But that was wrong, and we may never recover from the damage done because of that mistaken belief. In 2013, University of Zurich economist David Dorn and U.S. economists David Autor and Gordon Hanson co-authored an influential paper about what has come to be known as the “China Shock.” They showed that when local industries faced a surge of competition from cheap Chinese goods, the job losses were stunning.

As Dorn points out today, another bit of economic dogma — that people would simply transition to other jobs, or move to other places where there were jobs — didn’t materialize, either. And the shocks are long-lasting. Economists, including Raj Chetty at Harvard, have shown the devastating effects on children in communities where parents are out of work. “The work is still ongoing to understand why all of this plays out,” Dorn says. (Somewhat ironically, one prescient economist was Samuelson, who in 2004 turned against free trade, much to the horror of his peers. The core of his argument was that it was not win-win.)

There are also other costs to unfettered trade that simple economic models can’t capture. If your biggest trading partner, to whom you have opened up your economy, is actually your adversary, and is playing by its own set of rules, then perhaps you might want to rethink some of your openness.

Then there’s the pandemic, which revealed how fragile global supply chains are. When you need something, whether it’s a mask or a syringe or a semiconductor chip, it’s helpful to be able to make it in your country. If tariffs encourage local manufacturing — and bring jobs with them — then they might be worth some of the costs. That’s all the more true if the manufacturing and the design are intertwined, which is yet another thing we got wrong. “One of the critical conceits that our bipartisan consensus made over the last 40 years is that you can separate the manufacture[r] of things from the design of things,” JD Vance, now vice president-elect, said in a CNBC interview. That’s part of the thinking behind the Chips Act, which is supposed to bring semiconductor manufacturing back to the United States.

While most economists believe that increasing tariffs will raise prices and exacerbate inflation, it’s also less than crystal clear how it all works. In a recent paper, Alberto Cavallo, an economist at Harvard, showed that contrary to expectations, on goods that the United States imports from China that were subject to tariffs, the prices paid by consumers didn’t actually rise that much, at least not initially. Instead, U.S. importers and firms were bearing much of the cost. “This suggests that retailers are absorbing a significant share of the increase in the cost of affected imports by earning lower profit margins,” Cavallo writes. There are plenty of reasons this could be the case, including that the tariffs haven’t been around for long enough to know. But, as he also writes, “relatively little is known … about how economies in practice respond to tariffs, particularly when these trade policies involve large countries.”

Unfortunately, tariffs don’t always solve the problem they are supposed to solve, either. If only the equation were, impose a tariff and — presto! — jobs come back. They don’t, not always. Autor and Dorn’s paper shows that to date tariffs on foreign goods neither raised nor lowered U.S. employment in newly protected sectors. “There’s not necessarily symmetry between losing jobs through increased import competition and then trying to regain them via tariffs,” Dorn says.

All of which is to say, the role played by tariffs, including the role they might play in a broader industrial policy, is less than perfectly understood. The best example of industrial policy success, one that other countries have tried and failed to replicate, may be the happy accidental combination of government spending on defense technologies and entrepreneurship that created Silicon Valley. But then there are instances such as Germany’s effort to make East Germany into a mecca for solar panels, which got decimated by China, despite tariffs that were imposed from 2013 to 2018. The jury is out on U.S. efforts to rebuild semiconductor manufacturing, and on the European Union’s efforts to build its electric vehicle industry by imposing hefty tariffs on Chinese vehicles. “If you subsidize an industry but you can’t make it globally competitive, it will fail in the end,” Dorn says.

This would be easier to analyze if you could look at one tariff in isolation. But you can’t, because tariffs breed retaliatory tariffs, and compensatory subsidies, and a complex spiral ensues. For example, once China retaliated against Trump’s tariffs by putting its own tariffs on soy, Trump had to subsidize American producers of soy, confounding any clear takeaways. Chances are good, given the crony capitalism that prevails in modern America, that part of how the spiral of tariffs and subsidies would play out would be dictated by which industries can lobby the hardest.

But just as economists were wrong about the China Shock, no one can say for certain what the future will bring, either. “Unfortunately, economists, particularly neoliberal ones, overplay their cards when it comes to the knowledge we have,” says Luigi Zingales, a finance professor at the University of Chicago (and my co-host on a podcast called “Capitalisn’t.”) “It’s not always clear how tariffs work in a competitive global economy.” But fear of the unknown, combined with the logical belief that the unknown will be very bad indeed, explains why Zingales is sympathetic to economists who overstated the case for free trade. “One reason why there was such a strong consensus is because everyone is afraid of the slippery slope,” he says. In other words, the notion of finding balance is very fraught.

Free trade might not make the world perfectly safe, but it might still be a safer world than one in which trade wars proliferate. “The neoliberal elite understand very clearly that we could be in for a tragedy,” Zingales says. “Having the biggest guy on the block start to play the bully isn’t a good thing.”

So a targeted tariff that’s part of a broader policy could be the right thing to do, even if there are economic costs. But we need to be humble about what we don’t know and think in a nuanced, careful way about exactly what problem we’re trying to solve and what the costs could be.