To be fair, it's hard for the Dems to do anything effectively when a sitting president attempts to overthrow an election, fails, and then half of the voters think "You know what, I want that guy to lead our country again."
Not that they're blameless, of course - they had four years to throw Trump in prison, did nothing, and now we're reaping the result. But the problem goes much deeper than the Dems being incompetent. In a functioning democracy, voters aren't supposed to elect someone who literally committed treason, just because the alternative is "unlikeable" (what the fuck does that even mean, next to Trump).
All they needed to do was have a primary, but they didn't