Nearly 50 years ago, Daniel Ellsberg became one of the most important whistleblowers in American history when he released the top secret Pentagon Papers, about U.S. policy in Vietnam, to newspapers including The New York Times.

His actions are taking on a renewed resonance, with a new whistleblower playing a central role in the impeachment proceedings against President Donald Trump. Trump has denied any wrongdoing. Daniel Ellsberg’s archives were just acquired by UMass Amherst. While in Massachusetts to mark the occasion, Ellsberg, 88, spoke with WGBH Radio’s Arun Rath. This transcript has been edited for clarity.

Arun Rath: So let's start off by talking about your own actions as a whistleblower. The Pentagon Papers, for people who don't know, were a history of the United States' involvement in Vietnam. They showed that the government had not been entirely truthful about what was going on in Vietnam, and it had misled the public, as well as Congress. You said that thousands of people had access to that information, the Pentagon Papers, but only you came forward. Why you?

Daniel Ellsberg: That's puzzled me for a long time, why the others didn't or don’t in these situations. I've tried to understand it and I've talked to a lot of them. They don't want to lose their job. They don't want to lose their clearance. I had read the entire Pentagon Papers, 7,000 pages, 23 years of people advising the president that there was no way to make progress in Vietnam, that what each president was doing in turn was bound to fail. And yet he went ahead.

It was clear to me that Congress should have that information. And there was at that time no legal route, as there is now with the Intelligence Whistleblower Protection Act for the current whistleblower, that provides her or him with an authorized way to get that information to Congress. That didn't exist then. There was nothing but for me to copy that information and hand it to Senator Fulbright of the Senate Foreign Relations Committee, later to Senator Mathias or Rep. Pete McCloskey, each of whom promised to put it out, but then in the end decided to let me do it. And when it finally came out, I was faced with 115 years of a possible prison sentence.

Rath: Boston is where you turned yourself into the authorities. Does that flash through your mind when you come back here?

Ellsberg: If I were in front of the federal building, it certainly would. It was like an old program, "This is Your Life," with everyone you've ever known crowded into one room. In this case, it was a square, and the man who married us, and various people who had been friends of ours for years. They were all there to greet me when I came up after 13 days of eluding the FBI.

Rath: It seems that this whistleblower will not likely face legal consequences.

Ellsberg: A route exists now, which didn't exist in my day, for them to get information to Congress that Congress ought to have without facing prosecution. Ironically, in almost all situations, anything criminal will be classified. And once it's classified, it's criminal for someone to reveal it. It's a crazy situation, but there is this one route for getting it out, so she will not be facing prosecution as of now. I'm saying “she” just because everybody is assuming it's a “he” and I would like to find out, actually, it’s a “she." Many important whistleblowers have been women.

Rath: Legal consequences aside, in this particular situation with this whistleblower, their supporters are saying that they're still fearing for the whistleblower’s safety.

Ellsberg: Yes. There's good reason for that. I can speak from personal experience here. When President Richard Nixon was determined that I not put out the word that he was planning possible nuclear escalation against North Vietnam, indefinitely, the mining of Haiphong, which involved direct combat action, possibly involving Soviet ships and a Soviet crisis — he didn't want that out, and I was talking about it. So he brought 12 Cuban-American CIA assets from the Bay of Pigs up from Miami with orders to "incapacitate Ellsberg totally." And when I asked their prosecutor, William Merrill, 'Does that mean kill me?' He said, 'Well, the words were to incapacitate you totally.'

But you have to understand, these guys, who are all CIA people, don't use the word "kill" ever. They use euphemisms like “neutralize” — things that they might be overheard saying but wouldn't quite convey that what's being described as a murder. In my case, I think they just wanted me to shut up. I do think that with this whistleblower, the president doesn't know what else that person has to tell yet. He has painted a bull's eye on the back of that whistleblower, whenever she emerges, for his vigilante constituency to go after her. 'Rid me of this troublesome priest,' or this troublesome whistleblower, in this case. I think her need for anonymity is very real.

Rath: What advice would you have for the whistleblower at the center of all this right now?

Ellsberg: Well, at this point, it's assuming that she's told what she has to tell. The advice would be, she did the right thing and she knows what she's doing so far. I would say, get any further information she has to Congress, make sure that it does get out. And my thanks to her.

Rath: More broadly, you said that this impeachment inquiry into President Trump is about much more than Trump himself. Could you explain that? It seems like it's all about Trump.

Ellsberg: Well, I wouldn't say it's about so much more than Trump himself. It’s about more than this particular incident. The president's advocates want to say that this sort of thing is done all the time, and basically that's true. Why, then, pick out this particular one? Well, for the first thing, we have proof. Usually we don't find out. The president I worked for, Lyndon Johnson, absolutely was impeachable — should have been impeachable for lying us into a wrongful war. And by my silence, as with hundreds to thousands of others, I was complicit in that. So impeachment was absolutely right, but we didn't find out about that for years.

Much of the evidence for that was in the Pentagon Papers that I gave to Congress in 1969. That was five years later, and then didn't come out in the newspapers until two years after that. The other difference is quite important. This president, I think, violated the oath, as did Lyndon Johnson, that I took and every other employee took to support and defend the constitution of the United States against all enemies, foreign and domestic. Now, in violating Article 2, Section 8 that gives the power of deciding on peace or war exclusively to Congress, Johnson was violating that oath. And by my silence, I was violating it, as was everyone else. But I don't think that he was a domestic enemy of the constitution. He was violating it, he violated it when he needed to, but he wasn't trying to overturn it.

I think Donald J. Trump is a domestic enemy of the constitution. He doesn't believe in it at all. He believes that he is, in fact, a king. He believes what Richard Nixon expressed after he was out of office to David Frost — 'When the president does it, it's not illegal.' I can do what I want. He may not be the first to believe that, but he's the first where he's acted it out blatantly. He says things, by the way, I can say from someone who was an insider before, he says things that aren't unprecedented. Take his racism. Nixon was as racist as Donald Trump. And he said it over and over again, but in the company of his aides, not on All Things Considered. And this president will say things quite openly that other presidents would say only privately. I think the difference there is simply that he shows no awareness. Not only that there's matters of values and tact, let’s say, but questions of law. He's not clearly aware that in some cases he's simply violating the law. I suspect, by the way, that if he were tried on this particular incident, where he is clearly intimidating, coercing, a foreign head of state to help him in his election, I suspect he's sincere in believing there's nothing wrong with that. As he says, he doesn't have a sense of guilt. He doesn't have a criminal intent.