Trump ran for President as a publicity stunt. He behaved in an irrational, impulsive and abusive manner. When he won the Primaries, he thought, "Wow, this is actually working. Let's keep going." So during the election campaign, he continued to act that way, probably never believing he would win. But a lot of bad hombres ( Putin, Bannon,  Sessions) liked the idea of controlling a delusional president so they helped it along, often with bizarre results, the most bizarre being that Trump is now President. 
So he continues  to behave that way  ( Irrational, impulsive and abusive). He gave a coherent  speech to the join sessions and everyone thinks maybe he is normal after all. Well he isn't. The USA is embarrassing themselves  inside and out and is endangering  themselves and the world and protests not withstanding, they don't seem to realize how serious and perilous the situation has become.