People are overall more likely to vote Republican the richer they are, and to vote Democratic the poorer they are. The difference between a blue state and a red state is the income level at which that tips.
Since there's pushback I'll add: of course the reasons for this are subtle & complex! Ofc! But if you plot party votes against 1 variable--income--the link is consistent but red/blue states have different slopes
Yep. And mostly from the poorest or richest residents of SF? The association with income holds; it doesn't tell you where the break point from mostly Dem to mostly GOP is