Singer (pictured) and O’Hanlon are a yin-yang of the think tank world. O’Hanlon is a veteran strategy and policy hand, respected for his classically prudent approach to national security. Singer, on the other hand, has focused on how emerging drone and cyber technology will change national security, becoming a major policy shaper in his own right on 21st-century warfare. At age 29, he was the youngest senior fellow in Brookings’ history. Now 39, he has written four books on warfare, its impacts and its future. O’Hanlon, who earned all three of his degrees including a Ph.D. at Princeton, has nine books to his credit, was a leading analytical voice during of the Iraq and Afghanistan wars, and a budget and technology analyst in his own right. Both exude reason on budget issues and avoid the rhetorical flourishes — or gross exaggerations — that inhabit Washington security debates.