As Mayor they cannot hold on to the old jobs.
What they can do is look for the next way to get jobs into their cities.
I live in Pittsburgh. It took the dems here quite a while to respond, but eventually managed to come up with some workable ideas, (healthcare,, convention center, downtown more residential).
Yea, Dayton has tried to attract those types of business as well. Health care in particular.And Dayton has the largest employer in the state close by; WPAFB. Those hated "government" jobs.
However, there will never again be the numbers of good paying manufacturing jobs that provided a move up lifestyle for tens of thousands of people who lived in the Dayton area. Good jobs for people with a high school education. Good jobs that lasted from generation to generation. Those days are gone for Dayton and I would imagine Pittsburgh also. And there was nothing the Mayors could do about it. Even Mayor Mike Turner, who became the Repub Congressman from Dayton couldn't turn it around. So I don't think it is all on Democrat Mayors.