Trump says stupid things when he goes off-script...that is, when he starts "winging it".
His victory speech was CAREFUULY scripted by his team, and therefore was kind of decent and acceptable.
On the other hand, his many, many rally and campaign speeches were often ad-libbed, and therefore full of stupidity.
IF he stays on-script according to his advisors, then he will not look stupid.
However, his ego will probably get the better of him....