2018 is looking like an important off-cycle election in American politics. In the Senate, Democrats/Democrat-leaning Independents are defending a mammoth 26 seats (includes a special election for Al Franken’s old seat), and ten of those seats are in 2016 Presidential Red states. Of those, seats in Indiana (Donnelly), Missouri (McCaskill), North Dakota (Heitkamp, and West Virginia (Manchin) look particularly susceptible. On the other side, the Republicans are defending just eight seats, and only one is in a 2016 Blue State (Heller in Nevada). In addition to Nevada being a tossup, Arizona (to replace Flake) is also susceptible.

But what does the 2018 House prospect look like? The chart illustrates 80 years of House of Representative elections (1938 is the first year were the House popular vote is straightforwardly available). The location of the Red (Republican) and Blue (Democrats) bubbles in the chart indicate the percentage of seats each party held in each year. Anything above the dashed 50% line indicates a majority. The size of each bubble is proportional to the popular vote; the popular vote is normalized by the total US population for each election year. Bright red and bright blue circles indicate occasions where the popular vote did not match the seat majority. This includes recent examples in 1996 and 2012. A few things to note:

  • The US is now redder than people think: Since 1992, the Democrats have had the majority of House seats on just two occasions (2006 and 2008), though they won the popular vote on two further occasions (1996 and 2012).
  • The country used to be very blue: The Republicans were in the House minority every year from 1954 to 1994 (they lost the 1954 election, but won in 1994).
  • Democrats and 2018: The Democrats have won a single off-cycle election in the House (2006) since 1990. Will 2018 be any better?
  • Election turnouts: In Presidential years since 1938, 37% of the US population (not eligible voters) votes in the House elections. This drops to 25% in off-cycle elections.

Data and software: Data on the Senate 2018 race and historic House elections is taken from Wikipedia1,2. The data was compiled and visualized using Microsoft Excel3.


  1.  https://en.wikipedia.org/wiki/United_States_Senate_elections,_2018
  2. https://en.wikipedia.org/wiki/United_States_House_of_Representatives_elections,_2016
  3. https://products.office.com/en-us/excel