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Pro-business policies, tax incentives for productive residents, removal of government subsidized housing, and a general move away from forced diversity and political correctness toward a meritocracy.
ALL of these things, which USED to be “Republican” values would go a long way to salvaging ANY American cesspool, anywhere.
Additionally, the four examples you gave of liberal-run cities that are doing well, all benefit from tourism and other large net INFLOWS of cash from other areas of, not just the US, but the world at large. Boston, also has a huge and expensive higher education monolith, supported largely on enormous inputs of money from across the globe.
That is a LOT of spare cash for even wasteful, ignorant Leftist bureaucrats to play with.
All of those cities are heavy manufacturing cities with the exception of Galveston and New Orleans. Manufacturing is leaving for international reasons rather than local reasons. You can outlaw the Democrat party in those cities as well as subsidized housing and it would not change a thing with the exception of having shorter welfare lines and more empty buildings.
Using deductive reasoning and your statement then one would have to conclude that the most liberal city of San Francisco would then be number one dead city in America. Which is simply not true.
Boston and San Francisco both are research and development hubs which also generates cash flow. They are also nice places to live.