President Donald Trump believes that tariffs will shrink the trade deficit by getting more Americans to buy U.S. stuff instead of foreign stuff. But in economics, things don’t work quite that simply.

There was this “Simpsons” episode where Homer traveled back in time to the age of the dinosaurs: “As long as I stand perfectly still and don’t touch anything, I won’t destroy the future,” Homer said.

He obviously touches something, kills a bug and messes up the future, which he finds out when he gets back: “Don’t you remember Dad?” said Bart. “Flanders is the unquestioned lord and master of the world!”

Cue that classic Homer “D’oh!”

Economics is a little bit like that. Mess with one thing, something else gets messed up too. Take the trade deficit. The U.S. imports more than it exports. 

“The trade deficit reflects the difference between U.S. income and U.S. consumption,” said Mary Lovely, a senior fellow at the Peterson Institute for International Economics, which is a Marketplace underwriter.

More money going out of the house than coming in — we’re all just shooting dollars out the door to Temu, every day. Now if that was all that was going on decade after decade, we would have no money and the rest of world would have dollars just piling up, worth nothing. That’s not happening, because those dollars we send out into the world don’t stay there. They come back.

“They’re used to buy American assets,” said Matt Slaughter, dean of Dartmouth’s Tuck School of Business. “U.S. stocks, purchasing maybe corporate debt, they’re definitely used to buy U.S. Treasury securities,” he said.

Remember, when someone buys a corporate bond or a U.S. Treasury security, they are making a loan to that business or the federal government.

Now let’s imagine that the trade deficit was magically smaller. We’re sending fewer dollars out the door. So fewer dollars are coming back in the door as investments. Fewer loans to business, fewer loans to the government.

“If foreigners are buying fewer American assets, either the federal government has to borrow less or the private sector,” said Robert Lawrence, a professor of international trade and investment at Harvard.

A world with a smaller trade deficit is a world where this country is borrowing less, because there are fewer dollars coming in, because there are fewer going out. But here’s a problem: It looks like the federal government may need to borrow just as much as before or more because it may be spending more.

“All forecasts are they’re going to increase the federal budget deficit,” said Lovely at the Peterson Institute.

So if the government borrows just as much as before or more, the trade deficit is unlikely to fall — tariffs or no tariffs.

Some part of this economy would have to borrow less for the trade deficit to fall, and if it’s not the government, then there’s only one place left: the rest of the economy.

You know what makes the economy borrow and buy a lot less? A recession.