Michael Kazin is editor of Dissent and teaches history at Georgetown University. His latest book is American Dreamers: How the Left Changed a Nation.

For decades, Daniel Ellsberg, the leaker of the Pentagon Papers, has used his celebrated past to condemn the present. He has given hundreds of talks about the alleged crimes and deceits of every president from Jimmy Carter to Barack Obama; demanded the impeachment of George W. Bush; called on government employees to leak plans for bombing Iran; and been arrested on several occasions for protesting U.S. foreign policy.

None of this drew much notice from anyone outside of the anti-imperialist left. But now, in the wake of WikiLeaks and the NSA revelations, Ellsberg, the pioneer of Big Leaking, has become everyone’s commentator of choice. He does not disappoint. “In my estimation, there has not been in American history a more important leak than Edward Snowden’s release of NSA material—and that definitely includes the Pentagon Papers 40 years ago,” Ellsberg wrote in the Guardian. Ellsberg also regards Julian Assange and Bradley Manning as heroes and has raised money for WikiLeaks.

One can view such generosity as the latest act of anti-authoritarian solidarity by a 1960s radical or, less kindly, as an old man’s attempt to preserve and extend his legacy as the first American to pass explosive government secrets to the media. In any case, Ellsberg has been eager to bestow his blessing on Snowden and Manning and to echo their civil libertarian alarms. In the Guardian, Ellsberg wrote that Snowden “gives us the possibility to roll back a key part of what has amounted to an ‘executive coup’ against the U.S. constitution.”...