Democratic Prospects for the 2018 Midterm

Below, I look at the prospects for each party in the 2018 election. Overall, the House actually looks pretty good for Democrats, with many Republicans up for re-election in districts that Clinton won. The Senate is a different story, with many Democrats running in states that Trump won by a considerable margin. But who knows what will happen if the election becomes a referendum on Trump.

The data for this post come from The DailyKos. All the code for this post is available in a Jupyter notebook here, including the interactive plots and tables. I don’t have an in-depth understanding of politics, so it’s possible I’m missing some good indicators for midterm success. Let me know if you have any ideas for additions.

House Seats at Risk

The plot below shows the 2016 Deocratic presidential lead on the y-axis, and the 2016 Democratic House lead on the x-axis. Any point near an axis was a close race, with those on the positive side won by Democrats. Any point above the 45 degree line performed better for Democrats in the presidential race than predicted by the House lead.

Points in the bottom right quadrant are seats that are especially at risk for Democrats because Trump won these districts. In the top left are districts that were won by Clinton, so these might be the most likely to switch if the election becomes a referendum on Trump. Overall, there seem to be more Republican House seats at risk in 2018.

Close House Seats for Democrats

The first two numeric columns below show the Democrat’s lead in the House race and Presidential race for each district. When the sum column of these two values is negative it indicates a district that had a larger margin for Trump than for the Democrat that was elected.

Interestingly, Minnesota had a number of close seats, including the 7th district with a 35 point spread between Collin Peterson and Trump. Someone needs to ask these guys in Minnesota how they appealed to Trump voters (Peterson is a Blue Dog Democrat, and both Nolan and Walz are moderate Democrats). I think Walz provides an especially good template for moderate Democrats to follow in contentious districts.

I also include the Partisan Voter Index (pvi_2016), which combines the past two elections into an index of how the district votes relative to the country. Currently, the table is sorted by the ‘sum’ column, but Bokeh outputs interactive tables so feel free to sort the columns by any of the indicators.

Close House Seats for Republicans

I do the same thing below for House Republicans, but this time a positive sum indicates a district that had a larger margin for Clinton than for the Republican elected. I also include a column showing whether or not the Democratic Congressional Campaign Committee has indicated that this member of the House is a target for the 2018 election. This shows that the ‘sum’ column is a fairly good indicator for a midterm target.

Senate Seats at Risk

Next, I look at the Senate seats at risk for each party. Below is a plot similar to the one above, except it only shows the Senators up for re-election in 2018. This plot is also slightly different, as I am using the Democratic Lead in the 2012 Senate election for each candidate on the x-axis. This might not be the best indicator of the state’s support for the candidate as a lot has changed since 2012.

This plot makes it clear that Senate Democrats have a tough 2018 coming up. Many more Democratic Senators are below the 45 degree line, and 9 senators are up for re-election in states that Trump won.

Close Senate Seats for Democrats

The Senate is a little different because voting happens every six years. I order this by the sum of the Democratic lead in the 2016 presidential election and the Senator’s lead in their last election. A district could shift quite a bit during a Senator’s term, so this sum should be taken with a grain of salt.

These data make it clear that Senate Democrats have a very difficult election ahead in 2018.

Close Senate Seat(s) for Republicans

Relative to the Democrats, Senate Republicans have an easier 2018. Dean Heller’s seat in Nevada is the only one in a state that was won by Clinton in 2016, and many of the other seats look pretty safe.

So it seems clear that the Senate is much more difficult for Democrats, but who knows what will happen if Trump’s popularity rating keeps going south.

Special Elections Update - 2018

As an early 2018 follow up, I thought it would make sense to see how some special elections are going. I found this great dataset collected by The Daily Kos that includes every special election post Trump:

This scatterplot shows the Democratic margin in the special election plotted against the Democratic margin for the 2016 presidential election. Seats in the top left quadrant were lost by Republicans, while seats in the bottom right were lost by Democrats. As you can see, there are many more that have switched D -> R than R -> D, some by huge margins (Kentucky HD-49). Democrats generally seem to be overperforming the 45 degree line, suggesting good things to come.

So this bodes pretty well for Democrats in the 2018 midterms, although a lot can change in a year.