Across the board, in Senate, House and Governor's races, the wave boosting the Democrats crested about 10 days ago. Since then the advantage Democrats have built throughout the year has been reduced by from 1.5 to 3.5 percentage points. While forces are still a net positive to the Democrats, these forces are weaker than they were during the week before Halloween. This implies that the most competitive races will now be harder for Democrats to win and easier for Republicans to hold. This implies that the anticipation of a major surge to Democrats now needs to be reconsidered. While race-by-race estimates still show an 18 seat Democratic gain, and 27 seats as tossups (see our scorecard at Pollster.com here), this reduction in national forces makes it less likely the Democrats sweep the large majority of the tossup seats and could result in total gains in the 20s rather than the 30s or even 40s that looked plausible 10 days ago.
This cresting of national forces has taken place across Senate, House AND Governors races and occurred essentially simultaneously around October 25th. The estimators here, plotted as the blue line in the figures, is a measure of national effects that are common across all races. The estimate uses all polls in all races, but estimates the Senate, House and Governors races independently, yet produce similar results for each in terms of timing, though with some variation in magnitude. (For more on the estimation method, see this earlier post.)
As of last Thursday's data, the downturn was clear for the Senate but no indication of change had appeared for the House. Adding the polling data from Friday, Saturday and Sunday, the downturn is now apparent there as well. I did not do the Governors last week.
The congressional generic ballot does NOT show any such change (yet!). In my earlier post I cautioned that the generic ballot might not be reflecting a realistic assessment of the Democratic advantage. It may also not be reflecting the last minute dynamics of the campaign this year.
So what does this mean? The House still looks likely to go Democratic, but probably by a smaller margin that it might have a week ago. For a while, the Senate looked to come down to who won two of VA, TN and MO. Now MT must be added to that, and TN moved to lean Rep, perhaps requiring a Dem sweep of VA, MO and MT. (Momentum in VA remains pro-Dem, while MO is completely flat and MT is strongly trending Rep.) Possible but more of a trick that 2 of the former 3 states. The shrinking margin in MD may well end with a Dem win, but clearly some races that were viewed as likely Dem pickups or holds are now somewhat more in doubt that before, possibly including RI.
With two days to go there is a time limit on this dynamic. Reps may not have time to profit greatly from this trend, and we've seen sharp changes before so Dems may be able to recover (Republicans had a bad end of the week last week, after John Kerry and the Dems had a bad first of the week.) So no firm prediction here, but the evidence is that the Dems are falling back from their best chance of large gains.