Derek M. Scissors, a resident scholar at the American Enterprise Institute, said that China would be able to offset the effect of Mr. Trump’s tariffs through changes to its currency. However, any changes would have to be made gradually to avoid alarming investors and prompting capital flight, which could destabilize Chinese markets.

Mr. Trump’s trade actions have invited retaliation from Europe, Mexico, Canada and other countries, as well as China, taking a heavy toll on major American exporters, including farmers. In another Twitter post on Friday, Mr. Trump defended his strategy.

“Farmers have been on a downward trend for 15 years,” he said. “The price of soybeans has fallen 50% since 5 years before the Election. A big reason is bad (terrible) Trade Deals with other countries. They put on massive Tariffs and Barriers.”

Farmers have been struggling with lower commodity prices in recent years, but the price of soybeans has plummeted sharply since the beginning of May, as China, the United States’ biggest foreign buyer, threatened to curtail its purchases.

Though Mr. Trump has a strong base of support among American farmers, many insist that exporting is vital for their livelihoods and that trade pacts like the North American Free Trade Agreement, which the president has heavily criticized, have benefited them. American agricultural exports have nearly tripled since Nafta went into force in 1994, reaching $140.47 billion in 2017. They continue to outpace agricultural imports, which have also risen.

“Trade has been the one bright spot for farmers,” said Joseph W. Glauber, a senior research fellow at the International Food Policy Research Institute. “Until the tariffs were put on, farm exports have been near record highs in value.”

Ron Moore, the chairman of the American Soybean Association and a farmer in Illinois, said that tariff threats had appeared to have caused the market to collapse in recent months. “There’s extreme amount of volatility in the marketplace right now,” he said. “That really makes farmers nervous. We’ve all got bills to pay.”