Well, I can see you need some clarification here.
Allow me;
As of now, Trump is a business man. He is not the president, nor a man of legal power. Therefore, with the best interest of his company in mind, he is obligated to buy material from China. This is because China offers cheaper goods, and offers much more profitable deals to businesses in comparison to a similar supplier/manufacturer in the United States.
However, if he were elected president, his gears would shift, to have the best interest of his country in mind. He would garner better trade terms with China. He would increase domestic production. He would make the United states a bigger competitor in the market.
It is in this that he is able to show how China economically dominates the United states. Great entrepreneurs such as himself are forced to turn overseas to secure better trade deals. However, if elected president he could help change this, so that companies would be more inclined to do business with American companies.