Unfortunately, how countries use these capital inflows is not always so fruitful. In the United States, 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 their flip side) 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 U.S. 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 United States 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 United States. When a Malaysian company does business with a German company, in many cases it 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 United States 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 United States.

The roughly $500 billion trade deficit that the United States 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 byproduct of the central role the United States 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 fueling domestic booms and busts.