Presidents are coalition builders, not activists. The SJW movement is almost necessarily an activist movement, seeking to shift what lies within the mainstream of the political spectrum.
In other words, the kind of person who's likely to be a SJW and the kind of person who's likely to be president are different. In a scenario in which SJW views become mainstream, the self identified SJWs aren't as likely to become president as a bigger tent candidate who incorporates SJW views.
Anyway, at that point, I doubt most people who hold SJW views would call themselves SJWs. Its quite possible that the term itself dies out, even if the movement lives on.
Nobody actually calls themselves an SJW except maybe BRTD. It's usually an insult towards people who aren't bigots. I'm often tempted to call myself one, but then I remember that people often don't understand the sarcasm that's built into the term.
As for the question, never, because "SJW" is a meaningless term.