In addition to income, there are also correlations to race, education, gender, marital status, religion, gun ownership, etc. According to your source, support

In addition to income, there are also correlations to race, education, gender, marital status, religion, gun ownership, etc. According to your source, support of Democrats goes up with the amount of education; from 36% of voters who never went to college, to 57% of voters who have an advanced degree. That's a bigger spread shown than the rich/poor divide that you're focused on.