The republicans floated these rumors to Trump before the primary, which is probably the reason Trump at the time endorsed Luther Strange.
If that’s the case Trump/GOP had knowledge of this Moore allegations BEFORE the primary, then they had a moral/ethical obligation to confront Moore about this and if he wouldn’t out and out deny it, demand he immediately withdraw prior to the primary election or THEY would go public with allegations if he didn’t.
I personally don’t think these allegations particularly allegations with the then 14 year old girl is legit. Moore has been a public political figure in Alabama for decades and has had several statewide elections - this would have come out years ago if it was legit!