If he had worded his statement less strongly, I would agree with this one. "There is no way Trump can get a fair trial in D.C." is accurate enough, given demographics and a prosecutor's strikes. I have a hard time seeing the jury box not ending up with twelve people strongly biased against him.
"You could convict any Republican of anything in D.C." is a much stronger statement that doesn't follow. I suspect both that he knows better, and that he has said stuff like this before. He started his career as a defense attorney in the Air Force's JAG, then switched sides to the prosecution. I suspect that he became tired of sledding uphill against some of the most biased judges and juries on the planet, and probably said similar things about that situation.