President Trump knows a little something about debts from his business career.

Turns out, so does China. As both countries stumble into a tit-for-tat exchange of tariffs on a growing number of items within their massive trade flow, China appears to hold a, uh, trump card — almost $2 trillion in U.S. Treasury notes.

It’s a good investment for China, or anyone really. But that kind of relationship hands some sizable leverage to Beijing that’s uncomfortable for Washington.

China holds $1.7 trillion of the United States’ national debt, which this week totals $21.117 trillion.

That’s decreased $30 billion since last summer and is down 11 percent from China’s record holdings of $1.3 trillion back in 2013.

This makes China the largest foreign investor in U.S. debt and the second largest holder of U.S. debt overall after the Federal Reserve.

Japan is the second largest foreign investor in U.S. debt followed by, wait for it, Ireland. Overall, foreign governments own about $4 trillion.

If China wanted to up the ante in this trade dispute that Trump started, it could begin selling off some of its massive U.S. debt holdings. That would scare the market, decrease the value of the debt held by China and others and substantially raise the cost of borrowing and, in effect, running the American government.

“It is more effective as a threat,” said Jeffrey Gundlach of DoubleLine Capital LP. “If they sell, they have no threat. he added. “It would only escalate the situation and eliminate their leverage.”

Asked this week if China might dump some of its holdings in retaliation for Trump’s moves, a vice finance minister said his country is a responsible investor and will always safeguard the value of its own investments.