The leader of the United States encouraging law enforcement and the military to shoot American citizens for looting, that's the line.
And looting always leads to shooting, regardless of who is saying it.
Next, the 4th, 5th, and 6th amendments to the United States constitution. Telling armed forces to shoot unarmed people because they happen to be looting (e.g. when there is no imminent threat to life) is summary execution and unconstitutional.