Dems know what they are doing. This will solidify Trump for the primary season. Then once the general rolls around he will do a bunch of Trumpian stuff and irritate enough voters that he will lose to Brandon or a Buttigieg type Democrat.
That was initially what I thought, that the Dems wanted to make sure Trump was the candidate so that he will lose.
And that may be the long game. But, looking at the fear theater they’re staging (oooh, they’re calling out all the cops in DC, oooh, the evil Republicans are going to attack, oooh…), I think they may be going for something more immediate, such as the chance to declare some emergency, “suspend” our Constitutional rights, and give themselves unimaginable new powers.