Lots of talk about an 'act of war'. This was not an act of war, and I shall tell you why - because the 'victim' decided it was not. It does not matter what Russia does to the USA, it will only be an act of war if the US says it is, and indeed vice-versa.
This is important. The US is absolutely terrified of confrontation with Russia, and not because the US would lose, but because they would most likely very quickly start to win. The fear is what Putin would then do, with the obvious spectre of use of nuclear weapons. To that end, the US will, quite understandably, do everything they can to avoid such a scenario. However, the logical path of this argument tells us that even if the offence by Russia is more egregious, such as firing weapons on a manned US aircraft, and killing the crew, then the US will do everything it can to avoid it being seen as an 'act of war' which it could not allow to go unanswered by a military response.
My personal view is that in such a circumstance, the US would call it an 'accident', 'the actions of a rogue pilot', 'a weapons malfunction'... etc - they would deny that an overt act of war was indeed such, so terrified are they of the potential armageddon that could follow, and maybe they would have a valid point. I believe that Russia can do a lot worse that bringing down a drone, and that the US will find any excuse to not retaliate. Just my personal view.