One question we’ve put before these forecasters is which party will control the House and Senate. Here is the trend in the forecast over time:
Republicans are likely to lose seats in the House — ironically, thanks in part to the unintentional consequences of their attempts to gerrymander. But they have a good chance (85 percent right now) of retaining the majority.
The Senate, however, is a different story. The Good Judgment forecasters have given the Democrats better than 50-50 odds of gaining the majority for months now. This aligns with another prominent Senate forecast — from Drew Linzer at the Daily Kos — which currently projects a 50-50 seat split. Given Hillary Clinton’s strong chance of winning the presidency, Democrats would have a tie-breaking vote from Vice President Tim Kaine.
But note that these House and Senate forecasts have been fairly stable. There is not a lot of evidence that Trump’s falling poll numbers have brought down Republican candidates further down the ballot. This is as true now as it was back in June.
Some Good Judgment forecasts for individual races bear this out:
Of the three Senate races currently being forecast, two Republican Senators — Pat Toomey of Pennsylvania and especially Ron Johnson of Wisconsin — are in trouble. In both cases, their estimated chances of winning have trended down at least a little bit. Gov. Pat McCrory of North Carolina has also seen his estimated chance of winning slip below 50 percent.
On the other hand, Sen. Rob Portman of Ohio appears to be in a better position now: His estimated chances of winning have increased over time. This mirrors the trend in his polls, where he currently leads by five points. Of course, the forecast — a 65 percent chance that he will win — suggests this five-point lead isn’t certain to last.
With just under 3 months to go, all of this could obviously change. For example, 538’s Harry Enten sees some downward movement in the poll numbers of several Republican candidates for Senate.
For now, though, the results suggest that Trump’s impact on down-ballot races hasn’t emerged across the board.