It's about having a female Prime Minister, and being female in politics. It says this:
Even now women who choose politics have to decide how to define themselves in the context of gender in a way that would seem bizarre for men (although familiar enough to politicians from black and minority ethnic backgrounds).If I'm being generous, I'll say that it's contrasting women with men, and white people with people from black and minority ethnic backgrounds, and these two groups cross-cut each other (you can be both or neither).
If I'm not being generous, I'd say that 'men' here refers to 'white men', given that otherwise there's a weird contrast in that 'men' would find this situation bizarre but 'politicians from black and minority ethnic backgrounds', who are likely to be men, wouldn't.
OK, intersectionality is hard, and we haven't mentioned the fact that plenty of other sorts of people would recognise this disparity, but it is possible to avoid clumsiness like this.