President Trump. (AP/Darron Cummings)

If you call something “the worst trade deal maybe ever signed anywhere,” you kind of have to get rid of it when you have the chance.

So it seems like only a matter of time before President Trump really does begin to pull us out of the North American Free Trade Agreement so that he can try to negotiate a presumably “great deal” to replace it. The question, though, is what kind of deal this will be for American workers. And the answer may be not much of one.

Now, if you listen to populists of the right- or left-wing variety, everyone from Ross Perot to Sen. Bernie Sanders (I-Vt.) and Trump himself says there's one reason — and only one reason — that we've lost so many manufacturing jobs the past few decades. It's that the government has forced blue-collar workers to compete on unfair terms with people from much poorer countries. In other words, we've struck trade deals that have helped American companies outsource jobs to low-cost countries, but hurt American workers who have been left with only McJobs. “Our politicians,” Trump thundered during the campaign, “have aggressively pursued a policy of globalization, moving our jobs, our wealth and our factories to Mexico and overseas.” It was a familiar litany of acronym-filled woe: NAFTA, China joining the WTO, and the TPP. (Those last two are the World Trade Organization and the now-defunct Trans-Pacific Partnership).

“Trade reform and the negotiation of great deals,” Trump went on, “is the quickest way to bring our jobs back to our country.”

There's only one problem with this. It isn't really true. Trade deals, you see, matter, but they don't matter that much. What does is how strong or weak the dollar is. But let's back up a minute. This isn't to say that NAFTA, for example, has had no effect on our economy. It clearly has. Indeed, a decent chunk of our manufacturing base has migrated south of the border the past 24 years, although it would be an exaggeration to say that it was accompanied by a giant sucking sound, as Perot did. Even the most pessimistic estimates from the left-leaning Economic Policy Institute say that it cost us something like 400,000 manufacturing jobs and 100,000 jobs over this time. As economist Brad DeLong points out, those aren't even 0.3 percent and 0.1 percent, respectively, of our total jobs.

On the campaign trail President Trump spoke out aggressively against NAFTA, calling it "the worst trade deal maybe ever signed anywhere." Economists have a more nuanced view of the deal struck in the early 1990s. (Daron Taylor/The Washington Post)

That doesn't come close to explaining why we have a Rust Belt. So why do we? Well, a lot of it was inevitable, but the parts that weren't have more to do with bad dollar policy than bad trade policy. Think about it like this: Although our golden age of manufacturing employment is over, our golden age of manufacturing output is not. That's higher than ever. The simple story is that we don't need as many people to make as much stuff. Which, as DeLong highlights, is why the share of people working in manufacturing has fallen almost as much in Germany, which really has done everything right, as it has here.

But almost isn't the same as, well, the same. That difference matters. Economists, though, have a tendency to be a bit Panglossian about this, to shrug their shoulders about good, middle-class jobs being lost because it was all going to happen at some point anyway. It brings to mind John Maynard Keynes's admonition against giving ourselves “too easy, too useless a task” by saying that things will be all right in the long run, because we are all dead in the long run. Keeping factories here and the supply chains they're a part of offer people better wages, communities better stability, and the economy better productivity.

Why, then, haven't we been able to keep as many of our manufacturing jobs? Blame the dollar. It started when then-Federal Reserve Chairman Paul Volcker sent the dollar soaring by jacking up interest rates in his successful bid to whip inflation in the early 1980s. It continued when President Ronald Reagan's tax-cut-fueled deficits forced the Fed to keep rates higher than it would have for the rest of the decade. It went further after the International Monetary Fund bungled its East Asian financial crisis bailout so badly that emerging markets started stockpiling big war chests of dollars — pushing their value up — to save themselves from the same fate. And it's gotten going again now that the Fed is raising rates at the same time that the rest of the world is cutting them or even printing money. The point is that a more expensive dollar makes our exports more expensive overseas, and more-expensive exports can only be competitive if they become cheaper by moving production to lower-cost locales. That has been a bigger deal than the one we've struck with Mexico and Canada. Cutting tariffs by 5 or 10 percent just doesn't matter as much as the dollar shooting up 20 or 30 percent.

Which is to say that getting rid of NAFTA won't bring back many factory jobs if the rest of Trump's policies push the dollar up even more — which they probably will. That is, assuming Trump does in fact increase infrastructure and defense spending at the same time he slashes taxes for the rich and corporations. Just like the 1980s, the resulting deficits would force the Fed to raise rates more than it expected, and send the dollar up more than our exporters could afford.

Even the best trade deal maybe ever signed anywhere wouldn't change that. Sad.