They’ve been manipulating their currency for years. Decades.
Trump needs to tie the tariff rate to the yuan. Let them decide how much pain they wish to endure.
You're absolutely right. Just doing a simple search I found that back in 2010, China and Russia made an agreement to allow their currencies to trade with each other, and the article title said it would threaten U.S. dollars then. Back in 2015, they devalued the Yuan. In 2016, an article title was: World faces deflation shock as China devalues yuan at accelerating pace. Back in October 2017, they stated they would compel Saudi Arabia to trade oil in Yuan. In November 2016, they threatened to cut the sale of iPhones, and U.S. cars if President-Elect Trump pursued trade wars.