Here is the book:
And here is a blurb from that page:
"and Littell speaks of his friend's anguish at repeatedly failing the bar - and then he founded his own political magazine, which seemed only fitting because Kennedy yearned to live up to the family name and accepted that politics would be his destiny"
It doesn't specifically refer to the Senate seat Jr. was considering, but I am SURE that was what was in the magazine. I remember because I was shocked because I realized that was the seat Hillary got, and because I loved looking at Jr.