That's why there should be armed support on-call off-site. No problems, no call.
If there are problems, call the calvary!
I would be afraid that having armed support on call could end up escalating a fist fight into something much more tragic. Any such tragedy would certainly be spun to make us look bad even if the SEIU started it. I think a better idea would be to have the police aware of the protest ready to respond if there is any trouble.
I'm sure that Jesus will be with them in spirit, but for help on the ground, the CAVALRY might be a better option. ;o)