Recent special elections suggest Democrats may not ride a wave in November

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(CNN)Democrats have taken a tumble on the generic congressional ballot over the last few months. Their advantage in an average of the last five live interview polls is just under 7 percentage points, and it's even lower when you consider other polls.

The Democrats, though, have been taking solace in special election results since Donald Trump became President. In over 120 special congressional and state elections, they've been outperforming the partisan baseline based on the last two presidential elections by an average of 12 percentage points. A swing of greater than 7 points is generally consistent with Democrats taking over the House in November, though the exact break point is not knowable.
Special election results haven't been nearly as good for Democrats since the beginning of April, however.
In 25 special elections since April 1, Democrats have been outperforming the partisan baseline based on the last two presidential elections (or just the 2016 election in two Alabama special elections because of a lack of data) by an average of only 6 percentage points. The average is skewed by a few outliers. In the median special election since April 1, Democrats have been outperforming the partisan baseline by only about half a point.
    In other words, Democrats aren't doing any better in special elections over the last two months than the generic congressional ballot would suggest that they should be doing. In fact, their overperformance in recent special elections has been about half as high as it had been in all special elections since January 2017.
    This past Tuesday we saw Democrats lose by over 50 points in two special elections in Arkansas. Just last week, we saw a Republican pick up a Democrat-held seat in Pennsylvania's 48th District in the state House. That win received considerably less media attention than the Democratic pickup in the 178th District in that same body.
    It's not all bad news for Democrats, though, in special elections. They did much better than the partisan baseline in Arizona 8th's special congressional election, which was the special election with the highest turnout since April. It's not exactly clear how much we should read into special state election results, given they are usually low-turnout affairs.
    Further, Democrats did similarly to how they have done in April and May 2018 special elections during October and November 2017 special elections. Like now, they were overperforming the partisan baseline in those months, but not by a margin generally consistent with them gaining control of the House in November. After that slide in October and November 2017, Democrats climbed to their best position all cycle on the generic congressional ballot in December 2017.
    In other words, what we may be seeing now in the congressional ballot and special elections is noise. Democrats could easily recover in later special elections and on the congressional ballot.
    Yet we won't know if the recent Democratic downturn is "only" noise until later on. Special elections take place in a given time and place. The most recent ones have not been particularly strong for Democrats. If Democrats continue to perform as they have these past two months in special elections and continue to have good but not great generic congressional ballot numbers, talks of a Democratic wave need to be walked back.