The Democratic Congressional Campaign Committee has released Trump-Clinton polls for seven districts. The districts aren't among the nine that either Larry Sabato or Charlie Cook put in a lean/likely/safe Democratic column. They are among a next group of toss-up/lean Republican districts. If Democrats win all seven of these they probably net a minimum of 20 seats. While that isn't enough to take the majority, it's better than most projections now. The experts are saying Democrats +10-15, a number I agree with. Republicans picked up 13 seats in 2014 and their caucus was already a big bigger than it should be. In a neutral year Democrats should net 15 seats. Redistricting in Virginia and Florida alone should net them 2-3.
A congressional campaign committee releasing presidential poll results is odd. The narrative they are trying to push is that Hillary Clinton is winning big in these districts, so the Democrat in the congressional race must be too. If that were the case, then why didn't they release those results, the only ones that actually matter to the point they're making?
Probably because the polls don't show them doing that well. These polls have Hillary Clinton beating Donald Trump by 6 points in CA-10 and 12 points in CA-25. The California primary had heavy Democratic turn-out and the Democrats won these two districts by 13 and 14 points. Republicans beat Democrats in the two districts by 16 and 12 points. The primary showed us that people do split their ballots and that even if Clinton wins these two districts by 6 and 12 points the Democratic congressional candidate could lose by double digits.
There is actually a congressional number for the IL-10 poll. In that one the Democratic congressional candidate is winning by 6 points. In a district Hillary Clinton is winning by 31 points. That 25 point spread is actually very similar to the CA-10 and 25 spread in the June primary. The DCCC numbers lead me to believe that the typical margin between in the congressional race will be 25 points smaller than in the Presidential race. That'd mean Democrats would only win one of these districts.
I've long been skeptical of the idea that people don't split ballots but that's really going to be turned on its ear this year. We saw in primary polling that the same electorate that had Hillary Clinton beating Donald Trump by 7 points also had John Kasich beating her by 4 points. If those people would vote Republican down ballot with Kasich as the candidate then they aren't going to change their vote because they aren't voting for Trump.
Here's a poll that came out after I wrote this:
When you release an internal you release one that shows you up 17. This may have been released in response to Larry Sabato moving the district to “Likely Republican.” Internals are supposed to favor whoever releases them. So the horse race number should be taken with a grain of salt. This poll is, however, similar to the DCCC polls that showed a wide difference between the Presidential and congressional margin.