Ahh..I see what you mean.
The US has a history of using the Nat'l Guard for quelling disturbances, so I won't be surprised, nor particularly concerned for that matter, if troops are on alert. What will concern me if martial law and curfews are enforced without just cause. By this I mean, say if Guard troops were sent to Los Angeles or New York City and started martial law and curfew before any incidents sufficient to warrant calling the Guard in in the first place. I fear that could set a precident to allow, say curfew at anytime, all the time. That opens the door to a police state. Further, I would be concerned if there were roving squads out in rural areas not having anything of substance to protect; like a dam, power station, water course, etc.
I think however your "concept" perhaps may be utilized to a degree someday in the future if and when the US may seriously get in bed with the UN. But, UN uniformed troops running around? Not in our lifetimes, and I pray not in our children's either.