You don’t need it. D.C. is an exception to Posse Comitatus. What’s likely is the Guard will be activated but not on site. So they’ll be about 30 minutes away if the police are getting overrun again. But I would be very surprised if the Metro and Capitol Police don’t do an all hands day and even more surprised if a crowd got through that. It would almost certainly require a use of force by the crowd that rises to armed insurrection anyway. At which point the NG gets the go ahead and either the 82nd or 101st (whoever has the alert brigade that month) gets a mass recall text. They probably wouldn’t deploy but those options have to start lining up early to be ready in case some large organized militia actually turns it into a fight.
The chances of things getting that far are statistically indescribable but that’s the reaction chain.