[Joe Biden , Presidential Candidate:] These guys were attacking me and my family. I get it. And the press corps with me, they're all good people following me, they keep asking me, you know, they just brought up your son Hunter and they're doing this and that and the other thing. Well, guess what, I don't hold grudges because presidents can't hold grudges. Presidents have to be fighters, but they also have to be healers.
[Berman:] That's former Vice President Joe Biden responding, or in some ways not responding, after hours of attacks by President Trump's defense team, but his campaign, his staff, not being nearly so delicate. Arlette Saenz has been covering the Biden campaign on the trail. She joins us now live from Iowa City. And the campaign had a lot to say, Arlette.
[Arlette Saenz, Cnn Political Reporter:] Yes, they certainly did, John. And really this came as no surprise to the Biden campaign that President Trump's legal team would bring up Biden and his son Hunter Biden in their arguments. In fact, Joe Biden told me over the weekend he was expecting that they would become a focus. But you heard that very measured response from Joe Biden himself. But his campaign team did release a very pointed statement saying, we didn't realize that "Breitbart" was expanding into ted talk knockoffs. Here in planet earth, the conspiracy theory that Bondi repeated has been conclusively refuted. They added, Joe Biden was instrumental to a bipartisan and international anti-corruption victory. It's no surprise that such a thing an anathema to President Trump. Now, this is all coming as we are just six days out from the Iowa caucuses and those comments from Republican Senator Joni Ernst from here in Iowa, that's caught the attention of Biden's campaign, when Ernst said that she's interested to see if the Trump team's arguments is going to influence any Iowan's decisions as they head to caucus on Monday. And Joe Biden even responded directly to that late last night in a tweet. He said, Iowa caucus goers take note, Joni Ernst just spilled the beans. She and Donald Trump are scared to death I'll be the nominee. He added, on February 3rd, let's make their day. And this gets at the heart of what the Biden campaign thinks is going on here. They think that this whole episode shows that President Trump is most concerned about facing Joe Biden in a general election. And I have to tell you that here on the campaign trail, Biden's been getting a lot of questions from reporters about this, but we haven't heard questions in those question-and-answer sessions from voters directly about impeachment. And Joe Biden thinks this works to his advantage. He told us that every time Trump's team mentions his name in this trial, it gets him another vote here in Iowa. Alisyn.
[Camerota:] Arlette, thank you very much for the news from the ground there. So, we are six days away from the Iowa caucuses and Senator Bernie Sanders is surging. What's behind his rise in the polls? Let's get "The Forecast" with CNN's senior politics writer and analyst Harry Enten.
[Harry Enten, Cnn Senior Politics Writer And Analyst:] What is it? What is behind this?
[Camerota:] Don't pretend you don't know.
[Enten:] I you know, I like being a little coy. Don't you like being a little coy on a Tuesday morning? Take a look here. So
[Berman:] It's like the least alluring thing I have ever heard before 7:00 a.m.
[Camerota:] Oh contraire.
[Enten:] My girlfriend likes it in any event.
[Berman:] All right.
[Enten:] Iowa top choices for the Dem nominee. This is a "New York Times"Sienna College poll out this past weekend. Just take a look here. This is saying what we've been saying all along over the last few weeks. Bernie Sanders up to 25 percent. He was at 19 percent in October. He's up 6 points. Look at the slide for Elizabeth Warren from the last poll. She was at she's she's actually at 15 percent now. But whatever. She's at 15 percent now. She's down 7 points. Klobuchar up a little bit. But let's just take a look and sort of give you an idea of how the odds have shifted a little bit here and I think this is rather important. Adding that "New York Times" poll into the average, what do we see? We see Bernie Sanders chance up a little bit. Now he's at 6.5 out of 20 percent chance of winning. That's a little bit above Biden, 5.5 out of 20. But, again, here are the the key point here is Iowa polls are not necessarily that good. So even if Sanders is favored a little bit, he's not the overwhelming favorite.
[Berman:] Now, you've been digging, though, inside the numbers, because one of the big questions is why, what has Sanders done or what is happening that is leading to this surge in the polls?
[Enten:] So I think that there are two key reasons that Bernie Sanders has surged in the polls. He's getting his base back. Look here among very liberal voters. So back in September in our CNN"Des Moines Register"Mediacom poll, he was only at 20 percent among very liberals. Take a look at January, up to 38 percent. He's eating into Warren's base. She's dropped from 48 percent to 32 percent. Or take a look at the 2016 Sanders supporters. Remember, Sanders got nearly 50 percent of the vote in the Iowa caucus back in 2016. So just getting even half of that is a pretty substantial portion of the pot. And look at this, he was only at 25 percent in September. He's up to 44 percent now. Warren has dropped from 32 percent to 20 percent. So Sanders eating into Warren's base and getting a lot more support from very liberal voters.
[Berman:] He's winning back the people who supported him before at the expense of Elizabeth Warren. You get the sense the Warren campaign probably saw that before we did.
[Enten:] I think they almost certainly did. And that was with the attacks that you saw against Bernie Sanders over the last few weeks. Another key point here is that the moderate lane very, very tied up, very swished. They don't know exactly voters in those lanes don't know who to go for. So, look here, Biden at 23, Buttigieg at 20. You know, if Biden was basically cannibalizing that support, he'd be way up there. But the fact is, he's stuck there. And among the 2016 Clinton supporters, look at this, again sort of this clown car, 24, 19, 18, Sanders only at four. But when he's doing so well among his own supporters back in 2016, the fact that all these candidates are tied up together, it's just enough for him to do well.
[Camerota:] And aren't caucus goers notoriously hard to predict what they're going to do?
[Enten:] They are very they are very hard to predict, as you know. And I'll just show you this. I mean this is back on this date in 2016. Donald Trump led Ted Cruz by 6 points in the Iowa polling. Cruz, of course, defeated him. But, you know, it's so important to me, you know, the fact is that what we see right now in the Iowa polls, if Bernie Sanders were to win Iowa, he'd get a big bounce coming out of there. Winners get a medium 7 point bounce. But also expectation are a key thing that's going on here because for every point candidates outperform their Iowa caucus polls, they gain 0.7 points. For every point they underperform, they lose 0.7 points. And, of course, for Bernie Sanders, that's so important because right now he's just a little bit behind Joe Biden in the national polls. So winning in Iowa could, in fact, boost him up and he could take the lead in the national polls. But the fact is, because expectations are also higher for him right now, losing could really, really hurt him.
[Berman:] But he's leading in the polls in New Hampshire. He's strong in Nevada. It's possible Bernie Sanders it's not impossible for him the win the first three contests and then who knows.
[Enten:] Absolutely true. And then who knows.
[Camerota:] OK, Harry, thank you very much. You totally delivered on that.
[Enten:] Thank you. I try my best.
[Camerota:] Thank you. President Trump's plan for Mideast peace has been years in the making and today we will find out what it includes. But has a key player been left out of the process? That's next.