Due to the Posse Comitatus Act, would federal troops be able to respond? It’s not an insurrection. State level guard? Would anyone authorize the use of real anti-tank weapons? Would not be a pretty picture on the nightly news if they missed with a TOW or AT-4. Maybe try and trap the tank with heavy construction equipment? Or try and clear the area and let it run out of fuel.
Posse Comititus would not be in play at the time because they thought it was an military person in the tank. This makes it a totally military matter along the line of Mutiny or theft of property to commit a crime against persons. Posse Comitatus only applies to civilian and with out meeting certain criteria the military is not able to be involved.
MCRD San Diego had plenty of AT4's available at the ranges used to instruct the use of them. Depending on where they are, SWAT sends a copter to pick up an instructor at the range with a couple of them and bring them in to attack the tank.
I don't remember exactly where it was in the San Diego area, but some parts are on military reservations, USMC/Navy/USCG/US Army, even if people think they are in a civilian area.