Every Democratic campaign I've been old enough to understand could always be summed up with one sentence: "Vote for us or else the Republican will do evil things". A completely negative message, nothing about why I SHOULD vote for them, just about why I should vote against the Republican.
There's one exception. Obama 2008. This campaign was all about all the good things he was going to do, all the positive change that was going to happen. The word "Change" was so associated with his campaign, it was a meme for years. And Obama won by an absolute landslide.
Now, of course, Obama's actual presidency, he didn't do ANY of that, and instead, was just another war criminal, like every other president. But I do believe a big reason why libs deify him so much is his 2008 campaign, and I think that carried him to victory in 2012 as well. (Even though in 2012, they DID do a bit of that "vote for the Democrat or the Republican will do bad things, and if I was able to see that after they did that with Trump, but applied to fucking Mitt Romney, I would've laughed my ass off).
Now, after Obama was so successful with "change", and the good stuff? We had the complete opposite. Nothing will fundamentally change.
Democrats really hate learning, not just from their mistakes, but from the stuff they did correctly.
Think about the answer to this question, "What happens when a high visibility Democratic candidate loses? What happens to the high ranking staffers or contractors who run the losing campaigns"
Do they leave politics in disgrace? Are they viewed as pariahs whose opinions are shunned? Are they fired from their jobs as political consultants and Professional Poll Prognosticators?
Nope. Failure and losing don't matter. A political creature who loses spectacularly can still get jobs as consultants within their respective political crony groups. A consultant who runs multiple campaigns where their candidate loses goes on to work as a consultant in other campaigns. Both will make the rounds on talk shows and get gigs writing op ed articles and being hosts on political talking head shows. They might even "write" a book or two. They'll get invited to make speeches on college campuses or conferences for the political consultant class, of course getting paid for their time.
About the only way to be professionally ostracized is by intentionally burning all your bridges.
There are no real professional consequences for failure. So, it very literally is like sports ball. Two teams play against each other where one team is, by the rules of the game, going to "lose" the match. All that is required is that they show up to play.