Can you think of any senario where, say, an F16 couldn't deal with that has-never-happened situation?
Do you REALLY believe that is what the DHS drones are for? To be ready to attack an American snipering people from a building for terroristic purposes?
That's why the DHS also is purchasing 2700 of these:
To deal will all the Americans in the USA engaging in terrorist attacks. Did I get the analysis correct?