[incarcerated]

The President guilty of poorly ‘calibrated’ or poorly chosen words?
No. That isn’t the case.
The problem is not that the President used the word ‘stupid.’
The President is guilty of prejudging the Cambridge Police Department.

“Now, I don't know, not having been there and not seeing all the facts, what role race played in that, but I think it's fair to say, number one, any of us would be pretty angry; number two, that the Cambridge police acted stupidly in arresting somebody when there was already proof that they were in their own home…”

This is an instance of prejudice.

From Merriam-Webster:
Prejudice:
1: injury or damage resulting from some judgment or action of another in disregard of one's rights ; especially : detriment to one's legal rights or claims
2 a (1): preconceived judgment or opinion (2): an adverse opinion or leaning formed without just grounds or before sufficient knowledge b: an instance of such judgment or opinion c: an irrational attitude of hostility directed against an individual, a group, a race, or their supposed characteristics

To compound it, the President applied a stereotype about policemen:
“…and number three, what I think we know separate and apart from this incident is that there is a long history in this country of African-Americans and Latinos being stopped by law enforcement disproportionately. That's just a fact."

In this instance, the President is behaving as a bigot. That is the problem.