What I can gather from his Wikipedia page is that Kennedy, like Clinton was a good politician but a consummate womaniser. I have always wondered why citizens expect politicians to be 'moral' and whether 'immoral' politicians are necessarily bad leaders?
If a guy can't resist the temptation to break a promise he made to his wife for the sake of a few cheap kicks, it's less likely that he can resist the temptation to, say, hand out political favours to his favourite campaign donors.