that fiery debate between vice presidential joe biden and congressman paul ryan. We now know that 51 million of us watched. So, who won? And what does it mean for the presidential race? With just 25... See More
that fiery debate between vice presidential joe biden and congressman paul ryan. We now know that 51 million of us watched. So, who won? And what does it mean for the presidential race? With just 25 days to go before americans go to the polls, your voice, your vote. And our team is standing by, including the moderator of the debate, our own martha raddatz. But we begin with abc's jonathan karl right now. Jon? Reporter: Diane, it was an even harder fought than the presidential debate, but today, both men quickly hit the campaign trail, trying to take advantage of whatever momentum they can. Fresh off the big debate, joe biden rallied supporters in lacross, wisconsin -- paul ryan's home state. I am sure you observed last night, we had a little bit of a debate. Reporter: Ryan, out for a family breakfast in kentucky, seemed pleased, too. I feel great. Reporter: It was a debate that sets the stage for the campaign's final month, laying out big differences on the central issues. Like whether tax rates can be lowered without adding to the deficit. Not mathematically possible. It is mathematically possible. It's been done before. It's precisely what we're proposing. It has never been done before. It's been done a couple of times, actually. It has never been done before. Jack kennedy lowered tax rates, increased growth. Ronald reagan -- oh, now you're jack kennedy? Reporter: Biden went right at ryan over mitt romney's controversial comments calling 47% of americans who don't pay income taxes irresponsible. The idea, if you heard that, that little sol little quill on 47%, you think he just made a mistake, then I got a bridge to sell you. I think the vice president very well knows sometimes the words don't come out of your mouth the right way. But I always say what I mean. Reporter: When biden wasn't talking, he seemed oddly By our count -- smiling or breaking out in laughter 92 separate times. Expressive, often interrupting and occasionally personal. This is a bunch of stuff. Look, here's the deal. What does that mean, a bunch of stuff? Well, it means it's simply inaccurate. It's irish. It -- it is. We irish call it malarkey. Thanks for the translation. Reporter: And ryan needled ryan over the president's performance in last week's debate. I know you're under a lot of duress to make up for lost ground. But I think people would be better served if we don't keep interrupting each other. Reporter: Abc's martha raddatz asked pointed questions of both, pinning down biden on the administration's shifting accounts of the attack that killed the u.S. Ambassador to libya. Why were people talking about protests? When people in the consulate first saw armed men attacking with guns, there were no protesters. Why did that go on? Because that's exactly what we were told by the intelligence community. The intelligence community told us that. As they learned more facts about exactly what happened, they changed their assessment. Reporter: Ryan made clear it's an issue the romney campaign will hit hard in the campaign's final weeks. And that is what we are watching on our tv screens is the unraveling of the obama foreign policy, which is making the world more chaotic and us less safe. Reporter: Overall, ryan and biden were at their best last right. Biden showing his passion, ryan showing his seriousness. And one big reason for that, diane, is that we had a debate moderator who was able to bring out what these candidates are really about. So, if you don't mind, a little point of privilege, I would like to say kudos to my friend, martha raddatz.
This transcript has been automatically generated and may not be 100% accurate.