HARI SREENIVASAN, PBS NEWSHOUR WEEKEND ANCHOR: Joining me now from Santa Barbara, California, to talk about what the first presidential debate is "NewsHour Weekend" special correspondent Jeff Greenfield.

Jeff, I'm hearing Super Bowl-esque number potentials for the audience that might be watching this. And do most of us wait for the one-liners, the moments, the verbal and nonverbal communications? Or are we actually paying attention the whole 90 minutes or two hours, or whatever it is?

JEFF GREENFIELD, NEWSHOUR WEEKEND SPECIAL CORRESPONDENT: Certainly, not just the audience, but this army of journalists tend to look for that kind of moment. In fact, if you ask a journalist to recite the history of presidential debates, it would be, Nixon looked shallow. Ford prematurely liberated Poland from Soviet domination. Reagan said, "There you go again". Du kakis didn't seem it care if his wife was raped and murdered. George H.W. Bush looked at his watch. That's what always makes the next day's stories.

But I think that often it's the entire 90 minutes that viewers take away. If you think about the Obama-Romney debate four years ago, it wasn't any one moment that caused people to say Romney had won, it was the overall difference between what seemed to be a kind of defensive, sometimes petulant Obama and very assured, in command Romney. So, that's what I think you need to pay as much attention to as those moments.

SREENIVASAN: What about that level of expectation when Romney looked presidential and perhaps the expectation for Donald Trump is can he look presidential, can he contain himself for this period of time, is that a different level of expectation we have for him than say Hillary Clinton who has had such a long career in public service?

GREENFIELD: Yes, first of all, I'm developing an app which will deliver a nonlethal but painful shock to any analyst that says they have to appear presidential. You know, I always suggest someone should put on 200 pounds to look like William Howard Taft.

But more seriously, I think there is a danger of overstating the fact that Donald Trump is so out of the mainstream of candidates, you know, not only no public office but no civic engagement, that he is going to be held to a, quote, "lower standard". I think — I understand the point, but I do think that 90 minutes one-on-one with one of these two people is going to be president of the United States, and I'm not sure that a one-liner or a dismissive answer t a question about the complexities of say, dealing with NATO countries under attack is going to be enough for him.

You know, I think that if he after 90 minutes can't offer a coherent account of what he means, that's going to cost him.

SREENIVASAN: You in a former life have also helped candidates prepare for these events. Going into it, what would you tell both of these candidates today?

GREENFIELD: Well, I have to say, I do think that I would advise Hillary Clinton, it would be a much tougher — a much tougher piece of advice because it is true that what Trump is — I'm sure is being told is provide an answer that suggests you are familiar with the topic, and also counter her experience — this is what I once called political judo, take the strength as a weakness. If you are so experienced, why did you vote for the war in Iraq? How did we make such a hash of Syria and Libya?

Her challenge, I think, would be both to acknowledge error, and then say, but, you know, one of the key things you need to do as a president is to learn from your mistakes the way John Kennedy learned after the Bay of Pigs not to put too much trust in the military during the Cuban nuclear crisis. And then turn it and say, but one of your issues, Donald — and I think she might all him Donald — is you don't seem ever to admit a mistake. That's a very bad notion for a president.

The other thing, the oral history of the Gore-Bush in "The New York Times" today, and what happened apparently is both side agree was that Gore had such contempt for Bush's knowledge that he let it show in all those sighs and impressions of exasperation. And that's all everybody remembered from the first debate.

So, in the case of advising Hillary Clinton, there needs to be this fine line between trying to prove that she's smarter than he is, which would, you know, not be the right way to go, and then take his lack of knowledge and explain why that matters, that this isn't just a civics test. It's about, you know, governing as president.

SREENIVASAN: How about the role of moderator? What should Lester Holt be doing tomorrow night?

GREENFIELD: Well, you know, one of the things, you know, as I fantasize in my former non-virginal life as a political operative (ph), what would you do if 10 minutes into the debate, Trump turns to Lester Holt and says, you know, you're being very unfair?

All through the primaries, in fact Gingrich did this four years ago and it was many did this in the spring, particularly in the Republican primary, beating up on a moderator from the mass media, from the mainstream media, doesn't cost you any points. But in terms of Holt, Lester Holt, it's a very difficult position.

I think Jim Lehrer was right who moderated many of these debates saying this isn't an interview, because are you moderating a debate, what you need to do if you think that Donald Trump has stepped way over the line on factual matters which I think as a matter of fact he has, that to his opponent say, "What is your reaction to that, Secretary Clinton?" It is not his job to correct because then you wind up completely you know, unsettling the whole framework of the debate. I know that there are a lot of people who think that's what should happen particularly after the criticism leveled at Matt Lauer. But I really think it's a role that almost doesn't permit to do that.

SREENIVASAN: All right. "NewsHour" special correspondent Jeff Greenfield joining us from Santa Barbara — thanks so much.

GREENFIELD: Pleasure.