@AnarchoNinaWrites
I had a discussion with a friend a while ago where he was pretty sure Trump was bringing up Chicago for a generic racism dog whistle ( like Portland, or San Francisco are often shorthand, as you said), and he thought at the time that using Detroit would be too obvious.
Of course, we have moved on from such subtlety.
Detroit is about as likely to go red as DC. Hell, he's even going to Aurora tomorrow, and CO isn't going to suddenly go red- but he can do a racism there.