It has long been established that the federal government (like state and local governments) may, in certain limited circumstances, kill a US citizen on US soil without any formal process. Some familiar examples: a gun-to-the-head hostage situation, a mass shooter, and a person opening fire on law enforcement. In these scenarios, the perpetrator would typically be killed by law enforcement.
There are also circumstances in which the US military may kill US citizens on US soil. The Civil War is perhaps the best example. The Confederacy was not deemed a sovereign nation. Its soldiers were deemed US citizens engaged in criminal activity. When the US armed forces killed Confederate soldiers, they were killing US citizens without trial. I say this without an ounce of condemnation. It is just the bleak historical reality.
So it is clear that both federal law enforcement and the military may at times kill US citizens on US soil. But in the examples I've given, drones were not used.
Which returns me to my original question: Should drones somehow be treated differently? What about manned aircraft? Artillery?