It wasn’t just a photo, it was a yearbook photo. His stunt want just collecting dust in somebody’s drawer (like the photos of Barack Obama smoking pot).
People knew about his. But as with Harvey Weinstein and Hillary Clinton, they keep secrets because they like the politics.
And yearbook photos are totes OK to dredge up 30 or 40 years later.
I looked at my older brothers yearbook from a small private college in the midwest. It was chock full of Bongs and trays full of weed and the rest of it. Amazing. No KKK or black face pics though.