I would appreciate some sources on this as I could not find any for the demographics of DA voters so far (voters, not party membership).

It is true that the DA has won metros, but this amounts to a vote for service delivery and does not reflect confidence in the national leadership of the party. The discrepancy between municipal and national election performance is well-known.

I'm also not convinced that party membership is an accurate representation of voting patterns. How many people who vote DA are members of the party?

I'm yet to see a DA member stating that what Zille said offended them. One that isn't white, that is.