In Defying the Odds, we discuss the demographics of the 2016 campaign. College education has emerged as a major dividing line in American politics.
Warren has always relied heavily on the Connected Class. That includes doctors and lawyers, but, in general, it's the larger class of college-educated white people. This may, in fact, have been the biggest chunk of her support.
At her Iowa peak, when Warren was leading the field in mid-October, she was getting about 33% of all college graduates according to an Iowa State University poll, while Buttigieg was pulling in about 19%.
Now, Buttigieg is winning the college-educated vote 26% to 24%, according to the Iowa State University poll in December. If you were to screen out those with graduate degrees, and look at those whose highest degree was a bachelor’s (which is about a quarter of the Democratic electorate), we’ve swung from a 14-point Warren lead in October to a 5-point Buttigieg lead at the New Year.
Warren is falling mostly because white, college-educated voters are leaving her for Buttigieg.