It wouldn't take very many.
Remember, Dorner kept all of LAPD pinned down for weeks- even causing them to make huge public relations nightmares for themselves by firing on innocent people, and he was just a single guy with some mediocre tactics not even going after the head of the snake.
Imagine what hell there would be when you see small coordinated teams acting... it only takes a few and others might join in. You can expect the rulers to strike back in a hamfisted manner killing innocents in their wake. This is simply Guerrilla 101.
The guys who have already lost are the ones who decide they will turn in their guns or will wait for the SWAT team to show up to take them.
Yep, the "Troubles" in N. Ireland, and at times when the fight was taken to the rest of the U.K. in terms of bombings etc. and kept the RIC, Scotland Yard, and the MoD/SAS tied up for decades. There were only a dozen active bombers/triggermen at any given time, and roughly 10x more who were sympathetic and gave more passive forms of logistical support.
Looking at what Dorner did in L.A., or Lee and Malvo in the D.C. Metro..., or the Tsarnaev's in Boston, we don't need 3% which is the common mantra of the quasi militant Right in the U.S. right now, the figures of those "willing to actually fight" in the Revolutionary War. As little as .003-.0003% would wreak havoc and bring the country to a standstill and could be enough to get the whole ball rolling.
And if they had ANY veteran support, or advice from those in spec-ops, or from those versed in insurgency/counterinsurgency holy hell... If word of the aims or goals of any such ruckus got out, and it was clear they weren't targeting random civilians, but those pushing gun control, gun confiscation, or other un-American collectivist/Statist solutions, many police and combat-arms military units might even be sympathetic.
