Table 1 shows these gaps in the 2008 to 2018 elections — the numbers represent the percentage of each group that voted for the Democratic presidential candidate (or House candidate in midterm years). The largest of the four is the racial gap (i.e., the gap between white voters and non-white voters), which ranges from 32 points in 2018 to 42 points in 2008.

The latter came in the midst of Barack Obama’s first run for the presidency, with his candidacy turning out an extraordinary number of minority voters. The former was primarily the result of white voters favoring Democratic midterm candidates at higher rates than usual.

The second largest gap is between the youngest voters (below 30), and the oldest voters (65+), with the under-30 crowd being substantially more Democratic. That gap reached 21 points in 2008, when Obama’s campaign excited young voters.

The third and perhaps best-known gap is the gender gap: Women consistently vote Democratic while men more often favor the GOP. That gap runs from a high of 13 points in 2016 to a low of six in the Republican blowout of 2010. The final gap, education, is the newest. For decades, less-educated voters favored the Democratic Party at higher rates than those with a college education or better — but in recent years that trend has reversed. From 2008 through 2014 there was no education gap, but since then, college-educated voters have chosen Democratic candidates more frequently than have those without degrees.