I think back in JFK's time, it was not that unusual for rich people to "have people for that" so to speak. JFK had some pretty serious back problems, so for years his only sexual outlet was oral sex. He didn't want Jackie to do that, hence the "girlfriends". I bet Jackie was quite happy that somebody else would be taking care of that! She could just concentrate on high fashion and cultural events.

But in general, you are right. Obama was a real outlier. Most other politicians of every Party and Office are a horny bunch. Newt was getting BJs at the same time he was going after Clinton for that, and he cheated on every wife with the next one, before divorcing them. My local Congressman, Duncan Hunter, is about to go on trial for illegal campaign spending including taking random bimbos on ski trips. That's the main reason his wife took the plea deal and turned state's evidence.

I think there is some heady feeling of power and privilege people get when they get elected, that makes them think they don't have to follow the same rules as everybody else.