Obvious grain of salt, but someone I know that works (low level) in the RNC says they decided to go back in for Moore because their data shows he is very likely to win.
If hes likely to win, why bother embarrassing themselves and just let nature take its course? Moore could very well win, but I dont buy what your friend is selling.
If true, presumably to mend fences with Moore for once he is in the Senate so that he is somewhat more likely to play nice with the other Republican senators. I think the negatives for the RNC in running ads supporting Moore (versus just staying silent on the sidelines) are basically nonexistent outside of the political in-crowd. Whatever damage he does to the party is done by being the official Republican Party candidate and not being denounced publicly.