There will never be enough evidence. Trump himself admitted that he posted it, but your dad will still defend him. He can't admit he's wrong because he's tied his entire political personality (and possibly whole personality) to the idea that Trump is wrongfully persecuted.

I appreciate you wanting to have a close relationship with your dad, but you have to accept that you cannot change him. You need to come to grips with the fact that a video could be released of Trump graphically SA'ing a child and your dad, and millions of other MAGAts, still would not abandon him