The next two charts track how these changes have affected each party. Using the exit polls, they calculate how much of the total vote each of these three large groups provided in 1984, 1992, 2000, and 2012 for each party’s presidential candidate. In other words, they do not measure each party’s relative performance with each group, but their relative reliance on them—capturing the role of each constituency in each party’s coalition.

The results show that Democrats have grown significantly more reliant on minority voters, while Republicans are still preponderantly dependent on support from whites—including the white working-class voters who have rapidly declined as a share of the Democratic coalition.

As the first chart shows, even as the minority share nears 30 percent of the total presidential vote, nonwhites have increased only from about 2 to 10 percent of the Republican presidential vote since 1984. That has left the GOP relying on whites for nine in 10 of their votes, even as the number of white voters fall, providing only about seven in 10 of all votes. As noncollege whites have declined in the overall electorate, they have inevitably eroded as a share of the total Republican vote as well. But, especially given their diminishing share of the overall electorate, they still constitute a significant share of the GOP electorate. As the chart shows, in 2012, whites without college degrees still provided nearly half of all Republican presidential votes even as they continued declining toward one-third of the overall vote. That gap between the GOP coalition’s share of the white vote and the entire electorate’s share was even wider than in 1984.

Put another way, the increasing tilt of white working-class voters toward the GOP blunts the impact of their overall decline in the society: They are shrinking within the Republican coalition but notably more slowly than they are as a share of the total population. Even as they have plummeted by more than 40 percent since 1984 in the total electorate, they remain the single largest group of Republican voters—and, given the pattern of Donald Trump’s support, could solidify that advantage this year.

College-educated whites are growing in both the overall population and in the GOP coalition. They provided just over one-fourth of GOP votes in Reagan’s reelection, nearly two-fifths of the GOP vote in both 1992 and 2000, and just over two-fifths in 2012. That growth has come even though Democrats now generally run more competitively among college-educated whites than they did in the 1980s. Their increasing importance in providing GOP presidential votes reflects the overall increase in their numbers, the declining population of noncollege whites, and the inability of Republicans to build significant support in the growing minority population: In many ways, college whites have filled the space left by those other two groups.