What specific policies would help cities like Baltimore, Detroit, etc.

There are a number of “declining cities” in the U.S. These cities were former hotbeds of manufacturing and industry, but as manufacturing declined, the economies of these cities tanked, populations decreased, school systems suffered, corruption abounded, and many remain on a downward spiral.

Republicans often point out that these cities are mostly run by Democrats and that it’s liberal policy that is preventing these cities from improving. I don’t know whether that’s true or not. But I’m curious to know what people have in mind for specific policy reform that could actually benefit these cities? How would you “fix” Detroit or Baltimore or any other “rust belt” city?