From the Background: "The U.S.-China trade and economic relationship has expanded significantly over the past three decades. In 2018, China was the United States' largest U.S. merchandise trading partner (total trade at $660 billion), third-largest export market ($120 billion), and largest source of imports ($540 billion). China is also the largest foreign holder of U.S. Treasury securities (at $1.1 trillion as of April 2019 2018). However, tensions have grown sharply in recent years over a number of economic and trade issues."
CRS In Focus, IF10030
Congressional Research Service: https://crsreports.congress.gov/