On trade, I think it is possible he is bluffing. I.e. he just gives the impression of being a protectionist in order to scare China into also lowering their tariffs.
Some use to think that way, but it is becoming obvious that he is serious with his bad ideas. US business leaders are scared it will undo the help from lowered taxes.
...However, theoretically, if you can get everyone to lower their tariffs, that would be the best situation for everyone. I'm thinking Trump is known for being good at negotiating.
If he is serious, or if he is playing poker and loses, then yes, that will be bad. If I was God-Emperor of the US, I would go for unilateral free trade regardless of other countries...