On trade, What justificaion does the USA have to accuse China of 'selling too much not buying enough from USA'
The US president see’s trade as a zero-sum game, where there is always a winner and a loser, being the winner the one who sells more to the other. This view is not shared by most economists, as the mainstream opinion is that international trade is beneficial for both parties (see Ricardo or Krugman for examples). 

In the US’s president mind, “to win the game” they must restrict the sales of Chinese goods, using tarifs or quotas. The US can either produce these goods or import them elsewhere. The Chinese, however, are expected to have no other alternative but to keep importing advanced goods, critical for their economy, such as aeroplanes parts from Boeing. 

The expected outcome from this policy is less competition for national producers, potentially resulting in more jobs and higher profits. However, end consumers might end up facing higher prices for several goods, resulting in lower real incomes.