Transcript for Countdown Is On for Most Highly Anticipated Presidential Debate on Record
Good evening. And we begin tonight with the great debate. A night 18 months in the making. Some say it could be on par with the super bowl as far as the audience. Donald Trump arriving just moments ago, about to walk in and get a feel for that debate stage, giving a thumbs up there to the cameras. And here's a look at what you'll see tonight. We'll have it right here on ABC. Donald Trump will stand on the left. Hillary Clinton on the right there. And this number tonight. 1 in 5 Americans tell us, they could change their mind after what they see tonight. The new ABC news poll showing Clinton at 46%, trump, 44%, a dead heat. And the last time Hillary Clinton and Donald Trump spent this amount of time together, 11 years ago, at Donald Trump's wedding. Tonight, everyone is expecting a different atmosphere, so, let's get right to it. How Donald Trump is preparing, and here's ABC's Tom llamas. Reporter: Tonight, Donald Trump getting a feel for the stage that will soon become a political battlefield. Trump's debate playbook -- first, temperament. Something that has gotten him into trouble before. Look at those hands. Are they small hands? And, he referred to my hands, if they're small, something else must be small. I guarantee you there is no problem. I guarantee you. Reporter: Trump's goal? Look presidential. He's shown he can do it while still counterpunching, like defending New York values. When the world trade center came down, I saw something that no place on Earth could have handled more beautifully, more humanely than New York. Everybody in the world loved new York and loved new yorkers, and I have to tell you, that was a very insulting statement that Ted made. Reporter: Another challenge? Show command of the issues. This will be trump's first ever one-on-one debate. In the primaries, multiple candidates swallowed up air time. Tonight, trump will have to explain his policy solutions like his secret plan for Isis. But you have your own plan? I have a plan. If I win, I don't want to broadcast to the enemy exactly what my plan is. Reporter: And standing across from Hillary Clinton, the first female presidential nominee of a major party, trump may find himself again confronted with his past statements about women. You've called women you don't like fat pigs, dogs, slobs and disgusting animals. Your Twitter account -- Only Rosie o'donnell. Reporter: Trump was given video of Clinton's past debates. We'll shake on this. I want your signature. Reporter: Trump has to keep his cool. Even with the Clinton campaign planting a rival reality show billionaire front and center in the audience. Trump tormentor mark Cuban is bragging that he has a front row seat tonight. If he does, he'll be in the sight line of Donald Trump. Rudy Giuliani, one of trump's debate coaches, says trump did his homework, but didn't over prepare. He's basically going to be Donald Trump. Reporter: Also advising Donald Trump, former Fox News chairman roger Ailes, who famously prepped Ronald Reagan for the debate where he delivered this famous line. And I want you to know that also, I will not make age an issue of this campaign. I am not going to exploit for political purposes my opponent's youth and inexperience. Reporter: Trump says he's not rehearsing any canned lines, and insists he's won all of his debates just being himself. And Tom llamas live in that debate hall. Tom, you've been talking to the campaign. We love how you tried out that front row seat there. So much has been made about Donald Trump's temperament, and we remember what he told us right here on this broadcast not long ago. Wanted to get your reaction. What will your temperatement be on that debate stage? I can't tell you, because I'm not sure that I know. It will depend. You're going to have to adjust, you're going to have to see. You need flexibility. In life, David, you need flexibil flexibility. It may be very nice and respectful, it may not. All right, Tom, you've been working your sources. Any new clues tonight? Reporter: Well, Donald Trump says he wants this debate to be about issues, but if he is attacked, he will fire back. We know this morning he did some rapid fire question and answer sessions with his staff, and just before we came on the air, David, I was texting with his campaign manager. I said, any last-minute advise? She said, I told him to be yourself. David? All right, Tom llamas, thank you. Hillary Clinton faces a huge task tonight, as well.
This transcript has been automatically generated and may not be 100% accurate.