Over the past two decades, a dramatic shift has been taking place among Americans who think of themselves as either Democratic or Republican.

Less-educated voters, who through the 1990s and early 2000s tended to back the Democrats, have been switching to the Republicans. Meanwhile, those with college and post-graduate degrees have been moving to the Democratic Party.

While educational attainment has long been a strong predictor of party preference, recent surveys by Pew Research Center suggest that this trend is growing – particularly in the presidential race between Hillary Clinton and Donald Trump.

A survey carried out by Pew in August found college graduates backed Clinton over Trump by about three to one (59% vs 29%).

Voters without a college degree were more divided: 41% supported Trump, 36% Clinton.

If the gap between the education levels of Clinton and Trump supporters remains on 8 November, Pew says it will be the widest in any election for the past few decades.

The phenomenon is even more pronounced among white voters – 59% of white voters who did not go to college think of themselves as Republican or favour the Republican Party, compared with just 33% who identify as or lean Democratic.

As the first chart below shows, this is a big change from 2007, when the Democratic Party just had the edge over the Republican Party (48% vs 47%) among this group of voters.

Since 2008, the Republican Party has been steadily gaining support among white voters with some college experience but no degree.

The third chart, however, reveals a completely different trend among white college graduates. During the 1990s and early 2000s, they were more likely to back the Republican Party. But in 2008, 2012 and 2016, this group was almost evenly divided.

Image: Pew Research Center

The Pew research also highlights how the most well-educated Americans – those with post-graduate experience – have moved to the left over the past two decades: 31% hold ‘consistently liberal’ values now, compared to just 7% in 1994.

The gender gap in American politics

While women are more likely to vote Democratic than men, the contest between Clinton and Trump raises the prospect of the gender divide – as well as the educational divide – in politics becoming the biggest in any American election in recent history.

Image: NPR.org

The data for 2016 in NPR’s chart was based on polls conducted almost six months before the recent allegations about Trump making unwanted sexual advances towards women, or the emergence of a video in which he made lewd remarks about women.

Research by Pew, published in September, shows the gap between less-educated white male and female Republican supporters is at its widest for almost 25 years.

In 1992, 44% of both white men and women who had not graduated from college favoured the Republicans. Today, white men without a college degree (65%) are much more likely than white women without a college degree (51%) to align themselves with the party.

The gap between college educated white men and women, however, has remained pretty constant during the same period.

Although these trends have been a feature of US elections for some time, Pew’s research highlights the real and growing extent of the political divisions between Americans with and without a college education.