President Donald Trump delivered on a promise to label China a currency manipulator after its currency, the yuan, fell to its lowest value in more than a decade.

A weaker yuan, relative to the U.S. dollar, means Chinese goods can be exported more cheaply to the United States. A devalued Chinese currency, in turn, blunts the impact of Trump's tariffs on Chinese imports.

Trump applied the "currency manipulator" label to China in an Aug. 5 tweet, before the Treasury Department issued a formal declaration.

"China dropped the price of their currency to an almost a historic low. It's called 'currency manipulation,' " Trump tweeted. "Are you listening Federal Reserve? This is a major violation which will greatly weaken China over time!"  

The president's decision to label China a currency manipulator — which the United States last did in 1994 — represents an escalation of trade tensions with Beijing. Trump has long accused China of engaging in unfair trade practices, including intellectual property theft and the dumping of Chinese products on U.S. markets.

In a Treasury Department statement, Secretary Steve Mnuchin formally declared China a currency manipulator, as laid out under U.S. law. Mnuchin said Chinese authorities, who have "ample control" over the country's money supply, have openly acknowledged their central bank's ability to manipulate China's currency. 

The Treasury Department's determination requires, under federal law, that the department engage with the International Monetary Fund to address China's exchange rate.

The Trump administration's declaration that China is a currency manipulator moves this promie from Promise Broken to Promise Kept.