He was a nuclear-weapons historian who won the 2006 Pulitzer Prize for co-writing (with Kai Bird) "American Prometheus," a biography of Manhattan Project director J. Robert Oppenheimer.
He taught at Princeton, Tufts, and George Mason University.
He originally planned to go to medical school, but eventually switched to history. After graduating from Dartmouth, he served in the Navy for four years. He received a PhD from UCLA.