BLM people would have been arrested and many likely killed at their own homes weeks before the event based on the online chatter. Anyone that touched a barrier would have been gunned down on the spot.
I doubt it since they're already not being arrested/killed prior to attending protests right now, the ones in minneapolis, seattle etc. were all planned online and not preemptively halted
and in much of the protests the cops were not already there to defend the area, they had to actively take back territory so to speak, they're not that proactive
as posted above most deaths in the blm protests were citizens killing each other, not cops
also in this theoretical storming of the capital the context changes depending on whether this alt-universe trump is whipping them into a frenzy and saying I'll march with you to the capital, or if he's his normal self screaming at the cops to kill them, in which case they probably wouldn't be storming the capital in the first place