It isn't an allegation. It is a statement of observation. I'm not sure how friendly the new comment boards here are on the subject of external links. Try the Google search query "trump supporters demographics" or "trump supporter demographics". The first link for me was an Atlantic article that notes:

"For every 1 percentage point more college graduates over the age of 25, Donald Trump's share of votes falls by 0.65 percentage points"

PBS notes: "In an analysis of voters by education in states where exit or entrance polling is available, nearly half of those with high school diplomas or less schooling said they supported the billionaire."

CNN exit polling shows Trump won 69 percent of voters with a high school or less education. Contrast to only 51 percent support among those with postgraduate degrees. This is as regards the people who voted for him, mind you.

The Times looked into Trump demographics as well.

http://www.nytimes.com/2016/03/13/upshot/the-geography-of-trumpism.html