Comment: Bottom line: Can the govt use drone strikes on American soil?

Yes.
Holder's letter answered a specific question. In his letter he framed the question and answered it this way:
""Does the President have the authority to use a weaponized drone to kill an American not engaged in combat on American soil?" The answer to that question is no."
It does not rule out the use of a weaponized drone to kill an 'enemy combatant' (whatever that is) on American soil and in doing so will, in all probability, murder innocent Americans who will fall under the category of 'collateral damage' - and we all know what 'collateral damage' means.
So actually, Holder lied. Americans not engaged in combat will be killed by drone strikes on American soil. They just won't be the target.
I don't know why this point is being missed.