Yesterday, Apple sent the already wobbly stock market tumbling after lowering its earnings expectations for the first quarter of 2019. As of writing, Apple’s stock was on pace for its largest single-day decline in 6 years.

Since Apple is the world’s largest company by market cap — and this was the first time in over 15 years that the company slashed a quarterly earnings forecast — it behooves us to dive into CEO Tim Cook’s letter to investors to see what gives.

Here is a summary of what Cook wrote:

While we anticipated some challenges in key emerging markets, we did not foresee the magnitude of the economic deceleration, particularly in Greater China. In fact, most of our revenue shortfall to our guidance, and over 100 percent of our year-over-year worldwide revenue decline, occurred in Greater China across iPhone, Mac and iPad.

China’s economy began to slow in the second half of 2018. The government-reported GDP growth during the September quarter was the second lowest in the last 25 years. We believe the economic environment in China has been further impacted by rising trade tensions with the United States. As the climate of mounting uncertainty weighed on financial markets, the effects appeared to reach consumers as well, with traffic to our retail stores and our channel partners in China declining as the quarter progressed. And market data has shown that the contraction in Greater China’s smartphone market has been particularly sharp.

[…]

Lower than anticipated iPhone revenue, primarily in Greater China, accounts for all of our revenue shortfall to our guidance and for much more than our entire year-over-year revenue decline.” [Emphases added]

As Tim Cook’s letter makes clear, ongoing trade tensions are hurting the bottom line of the most successful company in the world. Those who think the U.S. is exempt from the economic hardships facing China (which just saw its first decline in manufacturing in over 2 years) must bear in mind that Apple is an American company, headquartered in Cupertino, Calif., that has created over 2 million jobs in the United States.

Kneecapping the most successful company in the United States is not putting ‘America First’ — despite what President Trump’s peculiar trade warrior Peter Navarro may claim.

Apple is far from the first company to state that trade tensions are negatively impacting their revenues. And the more China’s economy shows weakness, however much in part due to trade disputes, the more American companies are going to feel the pain. China is our largest trading partner — if their economy is decelerating, it spells trouble for us too.