But the wedge between the upper and lower classes isn't driven just by income, according to author and professor Michael Lind.
"Educational attainment is really the key to access the main sources of wealth and power and status, which is not just individual income; it's leadership and large organizations, corporations, and nonprofit bureaucracies, and in government," Lind said.
In his new book "The New Class War", Lind argues the rise of populism — from President Trump in the U.S. to the Brexit vote in the U.K. — is rooted in conflict between those with college degrees and those without them. Lind says the divide is evident among all age groups, including millennials — about 40% of whom have a bachelor's degree or higher.
"What you do find — and this is one of the sources of the new socialism and of the revolt on the progressive left behind Bernie Sanders, Elizabeth Warren, figures like that — is that you have 10 or 15% of the college-educated population is taking jobs that do not actually require a college diploma. And so there's a lot of frustration with the investment in a college degree that has not paid off in terms of work," Lind said.
The Democratic primary is full of different ideas on how to best address inequality. Sen. Bernie Sanders is calling for Medicare for All, Pete Buttigieg wants stricter rules on gig economy companies, and Sen. Amy Klobuchar is touting a housing assistance reform. Meanwhile, President Trump is expected to release a plan to cut taxes for the middle class sometime this year.
For Lind, none of those plans are a silver bullet to tackle inequality.
"I don't think any one person can do it. This is a matter of institutional reconstruction, largely at the state and local level," Lind said.