In Iowa, Rubio was especially successful in more urban, educated, places, while Trump and Cruz battled it out for the rest of the state. The results could be summed up by this narrative: Trump seemed to represent a shrinking, in part dying segment of America. Rubio represented the opposite — a growing, and more educated group of voters. Cruz's voters shared characteristics with Trump's, though the numbers didn't tell as dramatic a trend.
The patterns are clear in the following five charts, which illustrate relationships between how counties voted in the GOP caucuses, and their economic or social circumstances. Each circle represents one of Iowa's counties. The size of the circle corresponds to the number of votes that a candidate earned in that county.
The vertical position of a circle corresponds to the share of votes that a candidate earned in the county. The horizontal position of a circle corresponds to a statistic from that county, like the median wage or the percent of people with college degrees.
Where the relationship is so strong that it is unlikely to be explained by random chance, a blue line is drawn. (In other words, blue lines indicate correlations that are significant at the 5 percent level.)
1. Rubio won in more educated counties
This first chart confirms conventional wisdom about Rubio: He appeals to more educated voters. Both Cruz and Trump did poorly in counties where large fractions of residents had college degrees. Rubio, in contrast, claimed over 30 percent of the votes in counties where more than 40 percent of adults had graduated college.
These results are in line with entrance polls showing that Rubio is the most popular candidate among the college-educated.
2. Trump won in poorer counties
Similarly, there was a relationship between a county's economic vitality and its political leanings. Trump saw higher fractions of support in poorer counties. where the median annual earnings for a full-time male worker was around $35,000-$40,000 a year. Rubio, in contrast, got most of his votes from counties on the wealthier end of the spectrum, where typical men earn upward of $50,000 a year.
Support for Cruz didn't seem to vary much between poorer counties and richer counties.
3. Cruz was more likely to get votes in farming counties
Farming is still a big industry for Iowa, and Cruz did especially well in counties where a large fraction of people worked in agriculture. Rubio, on the other hand, struggled in places where farming is a big part of the community. Trump did, more or less, equally well in counties with a lot of farming and counties with relatively little of it.
4. Trump did better in counties with more dying whites
A high-profile study last year from Princeton economists Anne Case and Nobel laureate Angus Deaton found that death rates have been falling for almost everyone — except middle-aged whites in America. It's not clear why these people are becoming more and more likely to die, but this appears to have something to do with alcoholism, drug overdoses, and suicides.
Iowa, it should be remembered, is full of white people. In some Iowa counties compared to others, middle-aged white people are twice as likely to die. These are the same counties where Trump was more likely to succeed.
Rubio support showed the opposite relationship. His share of the votes was higher in counties where middle-aged whites were less likely to die. As for Cruz, there was no relationship between a death rates and the percent of votes he won.
5. Trump and Cruz saw the strongest support from places where people are disappearning
This final graph may be the most telling of all. Both Trump and Cruz — but particularly Trump — tended to do better in counties that have been losing residents over the past decade. Rubio, on the other hand, got most of his votes from places that are increasing in population.