But those pundits are ignorant. Suppose cops are guarding blocks 1 through 5. Rioters will then try mayhem on say block 6. So cops add more forces on blocks 6 thru 10. Then rioters hit block 11 and the pattern repeats.
You might say "just fill entire city with cops and troops", but then more extremists have access to more cops and troops to attack, INCREASING total attacks on cops/troops.
There are more "passive" extremists than active extremists. Passive extremists only act when they encounter their perceived enemy directly. If there are cops/troops in their front yard, they are fairly likely to act when otherwise they wouldn't bother.
Therefore, throwing quantity at the "problem" solves NOTHING, merely pouring gasoline on the fire.
If and when local authorities believe they need Federal assistance, they will ask for it.