I think he is reading that a lot of black voters feel some loyalty to the party establishment including Kamala. Many of these people voted against him in the primary, and he has been on a mission to unify the Michigan base since then.

Because his policy platform is solid, I think it's a fine move that won't lose him any votes. You wouldn't ever find me campaigning with Kamala ofc, but that's why I would never win a Michigan senate election.