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.
Replying to myself to add one caveat:
If he flees arrest, it will very likely destroy him. I figured he knew that and would accept what little jail time he might face from arrest as a sort of martyrdom, but the idea of going to jail really seems to have Trump pulling out all the stops, so the chance of him trying to flee is non-zero.