Monday is the final trading day of the first quarter. So far, markets have been volatile, thanks to all the uncertainty around tariffs — and by extension, U.S. growth. But the stock market isn’t the only thing that’s been falling this year. So has the value of the dollar.

Year to date, the greenback is down about 4%. That also reflects concerns about where the economy’s headed.

A lot of investors went into the year with a pretty optimistic outlook for the U.S. economy, said Juan Perez, director of trading at Monex USA.

He said they were hoping “that there was going to be a lot of policies coming from the Trump administration, and they’re pro-business, they’re pro-growth.” 

But then the trade wars kicked off, Perez said investors’ optimism quickly faded.

“The ultimate consensus is that trade wars will affect growth,” Perez said. “And right now, the narrative is very much not so positive for the United States.”

Investors who are nervous about economic growth often react by moving their money out of relatively risky assets, like stocks.

“And that flow, if it’s significant enough among enough investors, can actually alter the trajectory of a currency,” said Christopher Vecchio, head of futures and foreign exchange at the research company TastyLive.

He said that’s because U.S. stocks and other American financial assets are bought and sold in dollars. So when demand for stocks falls, demand for dollars does too.

Vecchio said a lot of foreign investors are starting to think twice about whether they want to invest in the U.S. to begin with.

“Those foreign investors have been selling their stocks. They’ve been taking those U.S. dollars, converting them back to euros, to pounds, what have you, and investing in their domestic markets once again,” said Vecchio. 

Another factor that’s been luring money away from the dollar is the yield on other countries’ government bonds, said Vishy Tirupattur, chief fixed income strategist at Morgan Stanley.

“So for example, in Japan, local currency government bonds in Japan are yielding meaningfully greater than what they were yielding six months ago,” said Tirupattur. 

The thing is, Tirupattur said tariffs could cause other countries’ economies to slow down too. And that means their government bonds might not keep attracting investors.

“The question really is: Will the tariffs weaken their growth prospects more? Would their central banks have to cut rates more than they would have otherwise?” said Tirupattur. 

And if that happens, the dollar’s value could start to strengthen again.