Trump is not saying that at all. Once again, your TDS is getting in the way of your ability to comprehend. What Trump is saying is that the Smithsonian & other museums only focus on the bad things about America and not the good things about America. In other words, museums are imbalanced.
So you are saying there is currently nothing good in our museums? I have been in many and thought there are some items hard to look at I have seen good and bad. You know, the complete story.
There tends to be an emphasis on the negative. Especially at museums like the Smithsonian. It's time to highlight more of the positive aspects of American History.