There are accusations of massaging the statistics as well. Most people in the know about DC say the place has terrible criminal activity daily.

https://freebeacon.com/democrats/is-dc-crime-at-a-30-year-low-mainstream-media-outlets-cite-police-data-to-say-yes-without-noting-a-commander-is-on-leave-for-allegedly-falsifying-that-data/

https://www.nbcwashington.com/news/local/dc-police-commander-suspended-crime-statistics/3959566/

As far as Trump going in, that's a debatable point. As far as it being a particularly nasty city from a crime standpoint. That's merely a well-known fact. It has been that way for many years and things are not getting better.