Blue upon blue

| Gabriel |

On Twitter, Dan Lavoie observed that Democrats got more votes for Congress but Republicans got more seats. One complication is that some states effectively had a Democratic run-off, not a traditional general. It is certainly true that most Californians wanted a Democratic senator, but not 100%, which is what the vote shows as the general was between Harris and Sanchez, both Democrats. That aside though, there’s a more basic issue which is that Democrats are just more geographically concentrated than Republicans.

Very few places with appreciable numbers of people are as Republican as New York or San Francisco are Democratic (ie, about 85%). Among counties with at least 150,000 votes cast, in 2004 only two suburbs of Dallas (Collin County and Denton County) voted over 70%. In 2008 and 2012 only Montgomery County (a Houston suburb) and Utah county (Provo, Utah) were this Republican. By contrast, in 2004 sixteen large counties voted at least 70% Democratic and 25 counties swung deep blue for both of Obama’s elections. A lot of big cities that we think of as Republican are really slightly reddish purple. For instance, in 2004 Harris county (Houston, Texas) went 55% for George W Bush and Dallas was a tie. In 2012 Mitt Romney got 58% in Salt Lake. The suburbs of these places can be pretty red, but as a rule these suburbs are not nearly as red as San Francisco is blue, not very populated, or both.

I think the best way to look at the big picture is to plot the density of Democratic vote shares by county, weighted by county population. Conceptually, this shows you the exposure of voters to red or blue counties.

Update
At Charlie Seguin’s suggestion, I added a dozen lines of code to the end to check the difference between the popular vote and what you’d get if you treated each county as winner-take-all then aggregated up weighted by county size. Doing so it looks like treating counties as winner-take-all gives you a cumulative advantage effect for the popular vote winner. Here’s a table summarizing the Democratic popular vote versus the Democratic vote treating counties as a sort of electoral college.
Popular vote Electoral counties
2004 48.26057 0.4243547
2008 52.96152 0.6004451
2012 51.09047 0.5329050
2016 50.12623 0.5129522

setwd('C:/Users/gabri/Dropbox/Documents/codeandculture/blueonblue')
elections <- read.csv('https://raw.githubusercontent.com/helloworlddata/us-presidential-election-county-results/master/data/us-presidential-election-county-results-2004-through-2012.csv')
elections$bluecounty <- ifelse(elections$pct_dem>50, 1, 0)

elect04 <- elections[(elections$year==2004 & elections$vote_total>0),]
elect04$weight <- elect04$vote_total/sum(elect04$vote_total)
dens04 <- density(elect04$pct_dem, weights = elect04$weight)
png(filename="elect04.png", width=600, height=600)
plot(dens04, main='2004 Democratic vote, weighted by population', ylab = 'Density, weighted by county population', xlab = "Democratic share of vote")
dev.off()

elect08 <- elections[(elections$year==2008 & elections$vote_total>0),]
elect08$weight <- elect08$vote_total/sum(elect08$vote_total)
dens08 <- density(elect08$pct_dem, weights = elect08$weight)
png(filename="elect08.png", width=600, height=600)
plot(dens08, main='2008 Democratic vote, weighted by population', ylab = 'Density, weighted by county population', xlab = "Democratic share of vote")
dev.off()

elect12 <- elections[(elections$year==2012 & elections$vote_total>0),]
elect12$weight <- elect12$vote_total/sum(elect12$vote_total)
dens12 <- density(elect12$pct_dem, weights = elect12$weight)
png(filename="elect12.png", width=600, height=600)
plot(dens12, main='2012 Democratic vote, weighted by population', ylab = 'Density, weighted by county population', xlab = "Democratic share of vote")
dev.off()

elect16 <- read.csv('http://www-personal.umich.edu/~mejn/election/2016/countyresults.csv')
elect16$sumvotes <- elect16$TRUMP+elect16$CLINTON
elect16$clintonshare <- 100*elect16$CLINTON / (elect16$TRUMP+elect16$CLINTON)
elect16$weight <- elect16$sumvotes / sum(elect16$sumvotes)
elect16$bluecounty <- ifelse(elect16$clintonshare>50, 1, 0)
dens16 <- density(elect16$clintonshare, weights = elect16$weight)
png(filename = "elect16.png", width=600, height=600)
plot(dens16, main='2016 Democratic vote, weighted by population', ylab = 'Density, weighted by county population', xlab = "Democratic share of vote")
dev.off()

png(filename = "elect.png", width=600, height=600)
plot(dens04, main='Democratic vote, weighted by population', ylab = 'Density, weighted by county population', xlab = "Democratic share of vote", col="blue")
lines(dens08)
lines(dens12)
lines(dens16)
dev.off()


m <- matrix(1:8,ncol=2,byrow = TRUE)
colnames(m) <- c("Popular vote","Electoral counties")
rownames(m) <- c("2004","2008","2012","2016")
m[1,1] <- weighted.mean(elect04$pct_dem,elect04$weight)
m[1,2] <- weighted.mean(as.numeric(elect04$bluecounty),elect04$weight)
m[2,1] <- weighted.mean(elect08$pct_dem,elect08$weight)
m[2,2] <- weighted.mean(as.numeric(elect08$bluecounty),elect08$weight)
m[3,1] <- weighted.mean(elect12$pct_dem,elect12$weight)
m[3,2] <- weighted.mean(as.numeric(elect12$bluecounty),elect12$weight)
m[4,1] <- weighted.mean(elect16$clintonshare,elect16$weight)
m[4,2] <- weighted.mean(as.numeric(elect16$bluecounty),elect16$weight)
m