Donald Trump believes that a half-trillion-dollar trade deficit with the rest of the world makes the US a loser and countries with trade surpluses like China and Mexico winners.

“They’re beating us so badly,” he has said. “Every country we lose money with.”

The reality is different. Trade deficits are not inherently good or bad; they can be either depending on circumstances. The trade deficit is not a scorecard.

What’s more, eliminating the trade deficit wouldn’t, on its own, make America great again, as Trump suggests. And trying to do so could mean giving up some of the levers of power that let the US get its way in international politics.

Getting rid of the trade deficit could very well make America less great. And the reasons have to do with the global reserve currency, economic diplomacy and something called the Triffin dilemma.

Imagine a world where there are only two countries, and only two products. One country makes cars; the other grows bananas.

People in CarNation want some bananas, so they buy $1 million worth from people in BananaLand. Residents of BananaLand want cars, so they buy $2 million of them from CarNation.

That difference is the trade deficit: BananaLand has a $1 million trade deficit; CarNation has a $1 million trade surplus.

But this does not mean that BananaLand is “losing” to CarNation. Cars are really useful, and BananaLandites got a lot of them in exchange for their money.

Similarly, it’s true that the US has a $58 billion trade deficit with Mexico, for example. But it’s not as if that’s just Americans flinging money across the Rio Grande out of charity. Americans get a lot of good stuff for that: avocados, for example, and Cancun vacations.

If you want to think of it in terms of winners and losers, in fact, you could justifiably reverse Trump’s preferred framing: “Those losers in Mexico gave us $58 billion more stuff than we gave them last year. Ha, ha, ha. We’re winners.”

It is true that a trade deficit subtracts from a country’s gross domestic product. GDP measures the value of goods and services produced within a country’s borders, so when a country is selling less stuff abroad than it buys from abroad, the country is making less stuff, and as a result there are fewer jobs. This piece of the Trump theory of trade is true.

But when a country runs a trade deficit, there is a countervailing force. Think back to our pretend countries. BananaLand has a $1 million trade deficit with CarNation. But that means that car producers in CarNation are sitting on an extra $1 million a year in income.

Something has to happen with that $1 million, and both of the two options have consequences.

One option is to keep that money at home. But keeping that money inside their own country will push the value of the CarNation currency upward. And as its currency goes up, cars will become more expensive in BananaLand — causing people there to buy fewer of them until eventually the trade deficit is eliminated.

If CarNation doesn’t want its currency to rise, it has to take that $1 million trade surplus and plough it back into BananaLand. There are different ways it could do that. People in CarNation could buy stocks or bonds in BananaLand, or companies in CarNation could invest in factories in BananaLand, or the government of CarNation could buy assets directly.

The choice is stark: A country running a trade surplus must either let its currency rise or let money flow back to its trading partners.

This isn’t just an abstraction. It’s what has happened between the US and China for the last couple of decades. China has had consistent trade surpluses, but it did not want its currency to rise in a way that would undermine its exporters.

So money has flowed from China into the US — both from the Chinese government buying US Treasury bonds and more recently in the form of direct investment from Chinese companies into the US.

When you see a headline about a Chinese company buying an American hotel group for $13 billion, you’re seeing the flip side of the trade deficit Trump bemoans. (The same when a citizen of China buys a luxury apartment in a Trump tower.)

Money flowing into a country is usually considered a good thing. It makes borrowing money cheaper, drives up stock prices and can mean more investment in new businesses.

So does a trade deficit mean fewer jobs? It depends on which force is more economically powerful: fewer jobs creating exports or investment dollars flowing into the country.

So which is it? It depends on what the country does with the investment that comes in.

In theory, that money could go toward long-lasting investments with positive economic returns: new factories and equipment; education for the workforce; and new roads and bridges; or repairs and improvements to existing ones.

Unfortunately, how countries use these capital inflows is not always so good. In the US, the influx of foreign capital in the mid-2000s went in large part to fuel an unsustainable housing and mortgage bubble. Greece’s capital inflows in the same time period went to fund bloated public spending.

When the world is flinging money at you, it’s important to use it for something productive. It’s not that trade deficits (and the capital inflows that are the flip side of them) don’t matter — but just knowing the numbers doesn’t tell you much about whether they are good, bad or indifferent.

Wouldn’t it be better if the US didn’t run a deficit?

It’s not clear that that’s even an option, because the dollar isn’t used just in trade between the US and other countries.

The dollar is a global reserve currency, meaning that it is used around the world in transactions that have nothing to do with the US. When a Malaysian company does business with a German company, in many cases they will do business in dollars.

When wealthy people in Dubai or Singapore’s government investment fund want to sock away money, they do so in large part in dollar assets.

That creates upward pressure on the dollar for reasons unrelated to trade flows between the US and its partners. That, in turn, makes the dollar stronger, and American exporters less competitive, than they would be in a world where nobody used the dollar for anything except commerce involving the US.

The roughly $500 billion trade deficit that the US runs each year isn’t just about poorly negotiated trade deals and currency manipulation by this or that country. It’s also, to some degree, a by-product of the central role the US plays in the global financial system.

There’s even a name for this: the Triffin Dilemma. In the mid-20th century, the economist Robert Triffin warned that the provider of the global reserve currency would need to run perpetual trade deficits to keep the world financial system from freezing, with those trade deficits potentially fuelling domestic booms and busts.

The key idea is that if a President Trump or any other future leader really wants to reduce our trade deficits in a major way, they’re going to have to rethink the very underpinnings of global finance.

There’s no doubt that being the global reserve currency creates costs for the US, namely a less competitive export industry.

But it also creates a lot of advantages. Lower interest rates and higher stock prices are one (though that has the downside of also feeding debt-driven booms and busts). Even more important is what the dollar’s prominence in global finance does for America’s place in the world.

It helps ensure that the US can afford to finance wars, and gives the government greater ability to fight recessions and panics. A country experiencing a banking panic will see money sent out of the country, causing its currency to fall and its interest rates to rise.

All that limits a government’s options for fixing the problem. In 2008, when the US experienced a near-collapse of the banking system, the opposite happened.

But it’s not just economics. “A lot of the benefits of having the reserve currency are more on the foreign policy side than the economic,” said Jennifer M. Harris, a senior fellow at the Council on Foreign Relations.

The centrality of the dollar to global finance gives the US power on the global stage that no other country can match. It has enforced sanctions on Iran, Russia, North Korea and terrorist groups with the implicit threat of cutting off access to the dollar payments system for any bank in the world that doesn’t cooperate with American foreign policy.

Part of what makes the US powerful is the great importance of the dollar to global finance. And part of the price the US pays for that status is a stronger currency and higher trade deficits than would be the case otherwise.

The debate over the trade deficit is about more than Mexico and China, cars and bananas, or winning and losing. It’s about what makes America great, and which of the country’s priorities should come first.

— New York Times News Service