Drawing from a database of more than 360,000 US registered voters over the past 25 years (including more than 12,000 in 2018 and 2019) the Pew Research Center studied long-term trends in party affiliation that found an increasingly divided electorate based on key demographic variables, making voter preference more predictable according to specific profile.
The survey found that Republicans hold wide advantages in party identification among white men without a university degree, residents of rural communities in the South and Americans who frequently attend religious services.
Conversely, Democrats maintain strong advantages with African-American women, urbanites in the Northeast and the religiously unaffiliated.
Among all US registered voters, 33% identify as Democrats and 29% as Republicans, while 34% of registered voters identify as independents. There has been little change in party affiliation since the 2016 election, with the exception of 2017, when there was a drop in the share of voters identifying as Republicans.
When considering partisan sympathies of independents, 49% of registered voters identify as Democrats or lean Democratic, while 44% of the electorate affiliate or lean Republican.
The typical demographic profile of a Democratic or Republican voter shows stark divides on race and ethnicity, education, gender, age and religion between the groups.
In terms of race and ethnicity, 53% of white (non-Hispanic) voters identify with the Republican Party or lean Republican. Increasingly, white voters constitute a shrinking share of the US electorate, from from 85% in 1996 to 69% in 2018/2019. Similarly, the growing diversity of the US electorate has meant that Four-in-ten Democratic registered voters are now nonwhite (black, Hispanic, Asian and other nonwhite racial groups), compared to 17% with Republican voters.
Levels of education has also become a predictive variable of voting habits, with Democrats increasingly dominant in party identification among white college graduates, in addition to even stronger support among university-educated African-American, Hispanic-American and Asian-American voters. Republicans maintain strong leads among white non-college voters, making up a majority of GOP voters (57%).
Religiosity and religious affiliation increasingly impact US voter preferences, as Christians make up about half of Democratic voters (52%) in 2020, in contrast to 2008, when approximately three-quarters of Democrats (73%) were Christians. The share of religiously unaffiliated Democratic voters have doubled since 2008, from 18% to 38%. For Republican voters, Christians constitute 79% of the party's support, down from 87% in 2008
Age and generational divides have also become an important factor in voter preferences, with those 50 and older making up majority of Republicans (56%), and half of Democrats. Millennials (ages 24 to 39 in 2020) are more Democratic leaning than previous generations, according to the survey.
Both parties are also increasingly divided along gender lines, with 56% of US women aligning with the Democratic Party, compared to 42% of men. Controlling for education, it was found that women who have not completed college are 11 percentage points more likely than men to identify as Democrats, while the gap is larger among educated women (65% of women, 48% of men).