Three of the last six national polls have found sharp downturns in the Democratic lead on the congressional generic ballot. After rising steadily since the week before the Foley scandal, the Democratic advantage has now begun to turn down. USAToday/Gallup, ABC/Washington Post and Pew Research Center all find substantial drops. Newsweek, Time and last week's CBS/New York Times polls do not find that decline, but rather show stability at around a 15-point Democratic lead.
While these shifts this MAY signal a sharp change of opinion going into the weekend, the magnitude of the drop is quite uncertain with only three polls. We routinely see lots of variation across polls, especially when looking at the generic ballot margin. Nonetheless, the shifts have been enough to convince my "local regression" estimator (the blue line in the figure) to turn down for the first time in a while. Since the blue trend line considers ALL the polls, it is not overly sensitive to single polls, though the combined weight of Gallup, ABC/WP and Pew is enough to move it down about 4 points, from +15 to +11 for the Dems. It is likely that the individual polls are overstating the extent of the downturn. The trend estimator captures the "signal" among all the "noise" from poll to poll. It would take more polls to "know" how much this downturn really represents. But the "poll" taken on Tuesday will answer the question for sure.
However, the current estimate of the Democratic lead based on the trend of all recent surveys remains at roughly +11. While down from the peak of early October, check my post and comparison graphic from earlier this week. The final Democratic advantage has not been over 10 points (or even close) in the last 12 years.