This is why the Gopvernment wants your gun.
So you cannot defend yourself from attacks like this.
A major form of tyranny involves making people dependent upon government protection, and then refusing to provide that protection when people are attacked by more-favored groups (see NYC Crown Heights riots, and multiple other examples).
One favorite story of mine from the Civil Rights era: A group says they are going to stage a march in favor of civil rights. The local police chief says he can't provide police protection. The march leader replies "OK, in that case we will bring our rifles and march armed". They got their police protection.