What Donald did here is tactically correct. He is not president yet. That means opening a relationship now is baggage free and can be walked away from without a problem. Trying to do this would be hugely problematic after he is in office.
Then it also solves another problem. It puts the Chinese off balance for what will be strenuous negotiations. Their whole strategy regarding the near ocean just got called. Rather silly to have a 'wall' when the gate is held by your main rival. This also gives the Chinese another huge problem. They have been running bluffs. They will now lose a lot of face backing down on these positions.
And it is now a given that Trump will call every such bluff.
I also have posted that the railway yard blast in China was likely a response by the US military to recent naval recklessness on the part of China. A very pointed message with zero face losing publicity.
Pence Defends Trump’s Call With President Of Taiwan, Says American People ‘Encouraged’ By Engagement