MSNBC is reporting that this morning there was a Fox News story about the bad neighborhoods in Baltimore and it was shortly it aired that Trump put out these tweets.
Trump is that bad boss who revels when those beneath him fail. Instead of offering to help, he enjoys and emphasizes the failure because he thinks it makes him look better. This is a crappy way to be a boss and a crappy way to be president.
Cummings represents Baltimore, but also Howard County, which is pretty white and affluent (Columbia/Ellicott City named one of the best places in the country to live; third in the country for household income). I’m sure they appreciate being called filthy and rat-infested.