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Time series of Democratic/Republican vote share in House elections

Yair prepared this graph of average district vote (imputing open seats at 75%/25%; see here for further discussion of this issue) for each House election year since 1976:

Decades of Democratic dominance persisted through 1992; since then the two parties have been about even.

As has been widely reported, a mixture of geographic factors and gerrymandering have given Republicans the edge in House seats in recent years (most notably in 2012 where they retained control even after losing the national vote), but if you look at aggregate votes it’s been a pretty even split.

The above graph also shows that the swing in 2018 was pretty big: not as large as the historic swings in 1994 and 2010, but about the same as the Democratic gains in 2006 and larger than any other swing in the past forty years.

See here and here for more on what happened in 2018.

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