NYC is a great example. Was a dump until Giuliani came in and became the gold standard city when Bloomberg took over for 12 years. He called himself a Democrat at the end, but they all hated him because he was pragmatic and got shit done. There was a tension there though and it worked out well.
DeBlasio came in and almost immediately things started to turn. As SF has consolidated power it has just fell off the deep end. Chicago has this story going for 50 years.