re: When did identity politics start in the US

i would say that's correct mid to late 80's and bill clinton being the last traditionally elected democrat.

the thing is identity politics is a fools errand in a country that's 70% white. the danger was always going to be the creation of a white voting bloc and the distribution of minorities in the united states isn't uniform ironically minorities are most concentrated in red states. take mississippi for example 37% of the state is black that's the highest percentage in the nation yet 90% of the white vote goes to republican's. a state turns red when 60% of the white vote accrues to the republican candidate and then that trend moves up and down ballot. romney lost because he under performed his national average among white voters (60%) in the mid west performing in the low 50's where as obama performed in the mid 40's. hillary clinton under performed obama among whites in the mid west by 7 points receiving only 38% of the white vote trump on the other hand performed to his national average among white voters right at 59%.

the notion that you can put together a coalition of fruits and nuts and win elections is sophistry.