This is a definitive work on Mansfield. I liked a lot of the stuff on his early life in the Butte mines and how he got his start. There's good stuff on how he managed to get himself through college. Moving on, I like how he worked against the buildup to Vietnam. We get excellent information on his friendship with Kennedy.
I skipped a lot of the later-60s and 70s stuff in this book, myself. I did appreciate that Oberdorfer looked into Mansfield's time with Goldman Sachs, as that company really screwed Montana with 1997's deregulation.
Supposedly Mansfield was just an adviser to Asia and hardly did anything. "I don't know why they pay me," he said at one point. He only had the job for a few years in the 90s, but I feel it's important as this firm is pure evil.
Anyways, good history with everything you'll want to know.