The other popular vote

Some observers say that the Republicans remain competitive only because they benefit from features of the American political system such as the Electoral College, equal representation of states in the Senate, and gerrymandering.   For example, this article in the New York Times notes the Democrats have won the popular vote in seven out of the last eight presidential elections and calls it "an unprecedented run of popular-vote success in U.S. history."   However, that's just presidential elections--during the same period, the Republicans have had majorities in the House of Representatives more than two-thirds of the time.  Is because Republicans have done well among voters or because of gerrymandering or clustering of Democratic voters in urban areas?  Nationwide vote totals for congressional elections are not routinely reported, but figures for 1946-2018 can be found in a report by the Brookings Institution. 

 It turns out that the Democratic share of seats in the House has exceeded their share of the votes in House races in 22 of the 37 congressional elections, but the advantage has shifted.  The figure shows share of seats vs. share of votes in two periods:

1946-1992 elections are in blue, 1994-2018 are in red.  The diagonal line is y=x, that is, share of the seats matches share of the vote.  Most of the points in the first period are above the line, meaning that the Democrats did better in seats than in votes, and most of those in the second period are below.  The Democratic advantage in seats in the first period may have been a result of the "solid South," which involved almost complete suppression of the black vote and low turnout among whites.  That is, the Democrats won a lot of Southern seats with low numbers of votes (even though they had high shares of the vote).  The current Democratic disadvantage probably reflects a tendency for votes to be "wasted" in non-competitive urban districts.  But whatever the reason, Democrats now are usually at a disadvantage in turning votes into House seats.  

The other thing to notice is the red vertical line, which marks equal vote shares.  In the first period, the points are almost all to the right of the line:  that is, Democrats got more votes.  Since 1994, this has changed--Republicans have gotten more votes in most elections.  The next figure shows the ratio of Democratic to Republican votes over time:

The Democratic share generally increased until the mid-1970s, then declined, before levelling off around 2000.  Although the swings in presidential vote shares from one election to the next have been small in the 21st century, swings in vote shares for the House of Representative have been fairly large--the 2010 swing was the largest since 1948.

I don't have any particular conclusion from all this--I just think it's data that deserves more attention.