The growth of the high-income Democratic faction can’t be perfectly measured—there is no database that exactly matches voters and their incomes—but there are plenty of ways to see the trend indirectly.
For example, a Wall Street Journal analysis observed the changing patterns of presidential voting in the 100 richest U.S. counties. The Democratic share rises over time. Walter Mondale carried just 7 of them in his 1984 landslide loss. In his 1992 victory, Bill Clinton carried just 36 of the 100. Joe Biden carried 57 of them in 2020…
In 2020, Democrats lost the vote of high-income households at the presidential level, according to exit polls. But I would caution against taking this too literally. Family earnings tend to rise with age and with marriage. An uncontrolled income comparison between younger Democrats and older Republicans can be misleading.
For example, compare a one-person household, a 25-year-old management consultant who earns $90,000 and votes Democratic, to a four-person household supported by a 53-year-old electrician who earns $110,000 and votes Republican. The Republican household makes more money, but only in absolute terms, not per capita. And it’s mostly because the electrician is older, and hence in his peak earning years. It’s not because he’s in a higher-earning profession.
My guess is that if you control for age, Democrats are already richer than Republicans. Regardless, Democrats are still gaining in exit poll share for high-income households, even if they are not currently winning it.