I think an indictment over the Stormy Daniels' payoff actually helps him a little. It's old news and it seems like a reach to make it a significant charge, and it gets the shock-impact of "Trump was indicted" out of the way long before the election. So, like Barr kneecapping the Mueller Report, it actually helps by lessening the impact of potentially more serious charges relating to document mishandling, Georgia, and his attempted coup.
I think the goal for Democrats is to make him a martyr with GOP primary voters to ensure his nomination, then beat a weakened Trump in the general. DeSantis will be a way more formidable foe.