In response to North Korea’s latest nuclear test, President Donald Trump on Sunday threatened to stop trading with any country that does business with the rogue nation.

However, that threat is almost certainly bluster, as such a move would have massive economic repercussions for the U.S. as well as the global economy.

Why? In one word: China.

North Korea’s economy is relatively small — the 119th largest in the world, according to MIT’s Observatory of Economic Complexity — with $2.83 billion in exports and $3.47 billion in imports in 2015. China is North Korea’s largest trading partner, accounting for about 85% of its trade volume — roughly $2.34 billion in exports and $2.95 billion in imports, according to MIT.

But China is also the largest trading partner of the U.S. In 2016, the U.S imported $462.6 billion in Chinese goods, and exported $115.6 billion to China. Eliminating business with China would be a tremendous blow to the U.S. economy and would almost certainly send retail prices soaring.

And it’s not just China. India accounts for about $1 billion a year in trade with North Korea — and does about $64 billion in business with the U.S. Pakistan, Russia, Thailand and the Philippines do tens of millions of dollars in business annually with North Korea. And while the amounts are small, even major U.S. trade partners such as France, Mexico, Brazil and Chile do business with North Korea.

Simply cutting off trade with all those countries would be virtually impossible, economically catastrophic for the U.S. and could potentially trigger a global recession.

The U.S. is much more likely to push for tighter sanctions against North Korea, while pressuring countries to reduce or eliminate trade with North Korea.

Treasury Secretary Steven Mnuchin said as much Sunday morning on Fox News. “It’s clear this behavior is unacceptable. … I will draft a sanctions bill and send it to the president. We will work with our allies. We will work with China. But people need to cut off North Korea economically.”

Meanwhile, Trump lashed out at the U.S.’s closest ally in the North Korean crisis — South Korea. In a tweet Sunday, Trump criticized South Korea’s “talk of appeasement” with North Korea, and on Saturday there were reports that the Trump administration was considering withdrawing from a five-year-old free-trade deal with South Korea. The U.S. and South Korea do about $115 billion in trade annually.