GEORGE STEPHANOPOULOS, THIS WEEK: You might remember Nate Silver from 2012. He's the forecast from fivethirtyeight.com. And his statistical take on the presidential election was dead on, correctly predicting how all 50 states would break. He's inspired all kinds of imitators. This time around, all of them are predicting a big election for the GOP. The New York Times giving the Republicans a 70 percent chance of retaking the Senate. Huffington Post at 74 percent, and the Washington Post puts GOP chances at a whopping 94 percent. Let's hear from Nate himself. Thanks for joining us, Nate. Saw your post this morning, 72 percent and climbing for Republican takeover.



NATE SILVER, FIVETHIRTYEIGHT.COM: Yes, we saw some new polls this morning in states like Georgia, Kentucky, that have further good news for the GOP.



Looks, it's still a close election. You have six or seven or eight races that can go either way. But like that poll in Iowa last night, which, as you mentioned, is one of the most reliable polls in the country. All these races are being held in purple or red states too. So the bar isn't that high. The polls are clearer now that the GOP will -- will probably win the Senate. We can bet (ph) a 73, 74 percent chance right now.



STEPHANOPOULOS: By this time in 2012, you had reached the point where you said it would take a systemic bias in all the polls, they would all have to be wrong for President Obama to lose. You're not quite there on Republican takeover of the Senate.



SILVER: We're not quite there. Because you can carve out a path for Democrats that goes through actually some red states, like winning in Alaska and Georgia and Kansas. Those states, the polls are all close or ambiguous or both. But it looks like in the swing states like Colorado and Iowa, Democrats are underdogs. They're almost certainly going to lose at least four seats. Arkansas looks like it's going the way of the other states like South Dakota that are very red to begin with. Louisiana, Mary Landrieu has a runoff, probably, so she'll have another month to campaign. But Democrats might have to bank on a runoff in Louisiana, a runoff in Georgia, and extending this campaign and winning some of those races as underdogs.



STEPHANOPOULOS: Finally, what's the biggest X factor, though? What Donald Rumsfeld might call the known unknown?



SILVER: I think it's the fact that people are not happy with either party. And you know, is there such a thing as an anti-incumbent wave? You're going to see for governorships, probably a lot of incumbents from both parties lose or come close to losing. So how do you square this kind of moderately pro-Republican mood with the very anti-incumbent mood? Could you have a Republican like Pat Roberts in Kansas lose, even though Republicans have a good night overall? So it's a multi-dimensional sort of election. Makes it a bit more complicated. But overall, signs look fairly poor for Democrats.