D's do need more black Senators and Booker as well as Ras Smith in a blue wave can win, in 500 days
It would have to be one heck of a blue wave for them to win Kentucky (and that wave will collapse if inflation ends up being more than a temporary blip). The state is not like Illinois or Pennsylvania where Dems can just boost turnout in the metro areas of Louisville and Lexington and win. They have to breakthrough in rural areas of the state or in places that lean Republican in Northern KY and Warren County. There's no way I see Booker's platform resonating well enough in those areas.
There are also those who were McGrath supporters in the last election who aren't happy with Booker because they argue he didn't do enough to support the ticket last fall. McGrath had no chance of winning anyway, but I don't see a Booker candidacy holding onto any ancestral Democrats or getting enough of them on board to do significantly better.