There are 3 possible scenarios at play here:
1) This is politically motivated. If so, history tells us that Pelosi and the Dems would be running to the podium to bash Republican hate and rhetoric. The fact they didn't implies that this isn't the likely case.
2) Its a completely random attack with no actual association to the Pelosi's. If so, then soft-on-crime policies promoting in SF are fair game for discussion, whether this was a crime of opportunity, or a mentally-imbalanced, homeless person, etc. Those are valid discussion points. I'd also ask, as you did, where is their protection?
3) This was someone that was known to the Pelosi's, and if so, the fact that the Pelosi's don't want to talk about it, and that the individual in custody wasn't named makes one wonder what was going on. What is Pelosi doing at 2:30 in the morning where he has violent guests over at his residence? At a minimum, it would raise questions about whom the Pelosi's associate with.
From my perspective, those are the 3 possible scenarios at play and thus the none of the speculations in this thread are inappropriate.