How do you explain the extensive list of failures of the Democratic Party in America's inner cities? They control them, farm the votes but conditions for Blacks only gets worse.
You're speaking too broadly. Not all big cities are controlled by democrats, especially in the South and Heartland. You probably don't know this, but you're using talking points from 60 years ago when FDR's New Deal Coalition controlled a much larger section of the country. Please be careful with the stuff you get from rightwing media, which keeps many of these old talking points alive for political reasons.
Having said that, I do think your comment has some legs.
I think the welfare policies of LBJ's Great Society, with the construction of inner city 'Projects' was misguided, and contributed to some of the ghetto'ization your are referring to. Of course, there was broad political support for this, but that was when both parties were more centrist.
Having said that, there are some other issues you might consider - and this is where you need to turn off talk radio, TV, etc., and dig deeper. Consider these points. The US rapidly deindustrialized starting in the late 70s. This is when capitalist production was shifted to Asia and the global south (see cheaper labor markets and non-existent environmental regulations). This contributed to the large superfluous populations in the inner cities, and it amplified the ghetto'ization that has destroyed many of our big cities. Also, there is the larger institutional trajectory of blacks: Slavery > Jim Crow > Welfare > Prison. The unintended consequence of slavery has proliferated into a series of institutional missteps - and the blame for this is deeply shared by both political parties.
Does this mean that Detroit wasn't mismanaged by the Left? Nope. It only means that you need to beef up your talking points so you can put some more meat on the sandwich you've been feeding us for too long.