His attacks on Cummings are easily refutable and have already been debunked. This is one of the few Congressman that has the ability to live fulltime in the district he represents and does so. He goes home everyday to his district and has sponsored legislation this year aiming to help his district. He has even gone to the WH to talk to Trump about passing said legislation. So yeah, Trump's initial attack was completely refuted a couple of minutes after he tweeted it.
Yeah, Baltimore has been on the receiving end of liberal legislation for many decades, for all the good that's done. I'd say that the legislation has done diddly squat to fix the terrible living conditions there, but the truth is that it probably helped create and sustain those conditions.