Daniel Ellsberg, famous for leaking the Pentagon Papers and his activism against nuclear weapons, announced recently that he has been diagnosed with terminal cancer. Mr. Ellsberg, now 91, copied the military’s secret 7,000-page history of the Vietnam War and gave it to The New York Times and The Washington Post in 1971. The government sued to stop publication, but the Supreme Court defended the First Amendment right of a free press against prior restraint. The papers produced a wave of anger at the government for having lied about the conduct of the war, which was already unpopular. In 1971, Mr. Ellsberg faced numerous charges, including violating the 1917 Espionage Act, but charges were dismissed in 1973 because of government misconduct. In 2021, he revealed that the government had drawn up plans to attack China with nuclear weapons during a crisis over the Taiwan Strait in 1958. With tensions rising between the United States and China, public distrust of the government running high and nuclear threats being lobbed over the war in Ukraine, his life’s work seems as relevant as it ever was. Mr. Ellsberg agreed to speak with Times Opinion at his California home about the lessons he’s learned. Q. As you look around the world today, what scares you? A. I’m leaving a world in terrible shape and terrible in all ways that I’ve tried to help make better during my years. President Biden is right when he says that this is the most dangerous time, with respect to nuclear war, since the Cuban missile crisis. That’s not the world I hoped to see in 2023. And that’s where it is. I also don’t think the world is going to deal with the climate crisis. We’ve known, since the 2016 Paris agreement and before, that the US had to cut our emissions in half by 2030. That’s not going to happen. Q. The number of people with the security clearances to view classified material has expanded, perhaps exponentially, since the leak of the Pentagon Papers, and I wonder, aside from a few people like Edward Snowden and Chelsea Manning, why haven’t there been more Dan Ellsbergs? Why aren’t there more people who, when presented with evidence of something that they find morally objectionable, disclose it? A. Why aren’t there more? It’s a question I’ve often asked myself. Many of the people whistle-blowers work with know the same things and actually regard the information in the same way — that it’s wrong — but they keep their mouths shut. As Snowden said to me and others, “Everybody I dealt with said that what we were doing was wrong. It’s unconstitutional. We’re getting information here about Americans that we shouldn’t be collecting.” The same thing was true for many of my colleagues in government who opposed the war. Of course, people are worried about the consequences. Before my case and the Obama administration’s prosecutions of whistle-blowers, they needn’t have been worried about going to jail. But apart from that, they fear losing their jobs, their careers, risking the clearances on which their jobs depend. People who have these clearances have often invested a lifetime in demonstrating that they can be entrusted to keep secrets. That trust becomes a part of your identity, which it is difficult to sacrifice, so that one loses track of a sense of higher responsibility — as a citizen, as a human being. Q. We tend to think of the classification system as a system of protection. But you sometimes talk about it, and I think correctly, as a system of control. A. That is what it is. It is a protection system against the revelation of mistakes, false predictions, embarrassments of various kinds and maybe even crimes. And then the secrecy system in its application is predominantly to protect officials, administrations from embarrassment and from accountability, from the possibility that their rivals will pick these things up and beat them over the head with it. Their rivals for office, for instance. Q. How should the average reader understand the difference between the importance of a risotto recipe that was disclosed by the Russian hack of John Podesta’s email account and serious secrets like those disclosed by Snowden? Steven Aftergood at the Federation of American Scientists, who studies secrecy, for instance, once called the indiscriminate disclosure of military files by WikiLeaks a kind of “information vandalism.” A. I disagree with Steve. I think he greatly underestimates the amount of overclassification. The media as a whole has never really investigated the secrecy system and what it’s for and what its effects are. For example, the best people on declassification outside the media, the National Security Archive, month after month, year after year, put out newly disclosed classified information that they have worked sometimes three or four years, 10 years, 20 years to make public. Very little of that was justified to be kept from the public that long, if at all. An expert estimated in Congress in 1971 that 5 percent of classified information met the criteria for secrecy at the time it was classified, and after a few years that decreased to half of one percent. Q. What’s it like to live surrounded by thoughts of nuclear war and unaccountable government? A. In my office, an assistant of mine once put up little labels to show parts of the bookshelves and especially the drawers in my files. And my wife came down and saw “genocide,” “torture,” “massacre,” “terrorism,” you know, “bombing civilians,” and she said, how can I be married to somebody who has files like this in the office? And so this is California, this is Berkeley, so a bunch of her friends came down with burning sage and exorcised my office. But that has been my life since I started work at the RAND Corporation in 1958. I think about nuclear war not because I find it fascinating but because I want to prevent it, to make it unthinkable, because I care about the world that it would destroy. Q. Robert McNamara, who was secretary of defense during the Cuban missile crisis, once said, “The indefinite combination of human fallibility and nuclear weapons will destroy nations.” Why haven’t we seen nuclear weapons used since 1945? A. We have seen nuclear weapons used many times. And they’re being used right now by both sides in Ukraine. They’re being used as threats, just as a bank robber uses a gun, even if he doesn’t pull the trigger. You’re lucky if you can get your way in some part without pulling the trigger. And we’ve done that dozens of times. But eventually, as any gambler knows, your luck runs out. For 70 years, the US has frequently made the kind of wrongful first-use threats of nuclear weapons that Putin is making now in Ukraine. We should never have done that, nor should Putin be doing it now. I’m worried that his monstrous threat of nuclear war to retain Russian control of Crimea is not a bluff. President Biden campaigned in 2020 on a promise to declare a policy of no first use of nuclear weapons. He should keep that promise, and the world should demand the same commitment from Putin. Q. How are you feeling? A. Great. I was appreciating life even before the CT scan, and then a couple of weeks later had an M.R.I. and then a second CT and was told I have three to six months. It has been said that it’s good to live each day as though it were your last, but that’s not really practical. Living this month as though it is my last is working out very well for me, and I can recommend it. I thought it was pretentious to say publicly, you know, well, I have pancreatic cancer. But my sons both thought I should share the news with friends, and that was also an opportunity to encourage them to continue the work for peace and care for the planet. As I said, my work of the past 40 years to avert the prospects of nuclear war has little to show for it. But I wanted to say that I could think of no better way to use my time and that as I face the end of my life, I feel joy and gratitude. The New York Times