That's the problem with the democratic party. it's a coalition of the spiteful. You have lbgt teamed up with muslims. crony capitalists teamed up with marxists. It's very difficult to lead a party where its various factions have adversarial agendas. If you appease one faction you hurt or piss off the other faction.
Nothing gets done beyond endless babysitting from preventing everyone from wanting to kill each other.
There's a long-standing joke about the situation: "I belong to no organized political party! I'm a Democrat." And that's why they make dumb decisions over and over and over again. They aren't looking at the outside world; they're looking at the internal politicking within the party. Try to look at it from a DNC insider's point of view: if you piss off someone with a lot of influence, they can leave and take their faction with them. True, running a shitty candidate has a good chance of losing, but losing is practically a sure thing if your guy gets Perot'd by a third party challenger that you failed to corral. Not to mention long term damage to the party, which is your personal source of power and employment, as well as it being an obvious failure that other people gunning for your job will exploit to kick you out and take your position for themselves.
All this is true for political parties in general, but the identity politics factions in the Democratic party make things worse than usual because by nature they can only see things only through the lens of their own grievances and are incredibly self-centered and are kept together mostly by hate for the majority. Also, there are a lot of them.
So, there's a ton of things you can't do. You can't piss off
any single large faction or its leaders too much, or they'll bolt, with consequences as described above. You certainly can't piss off
all the factions, or they'll remove you. You can't bring in an outsider, no matter how good their chances of winning may be, because it will piss off
everybody who's spent decades kissing ass and working their way up the party ladder. And
nobody in the upper ranks will
ever sacrifice their own career for the good of the party, because those sort of self-sacrificing people won't have a career long enough to
reach the upper ranks, and they can't parachute in from the outside either because of the problems above. If
anyone is apparently self-sacrificing in party politics, it just means that they've been secretly promised something good later as a reward for their forbearance.
So most of this trying to figure out what they were thinking, or what their plan was, in choosing these losers? Pointless. It's all about who was promised what, and how much internal clout they have to make good on those promises, and so on, and most of that only comes out years later if at all.