And so the question must be asked at this point: What is Putin's endgame here?

There doesn't need to be an endgame. Killing off a couple of longtime enemies while pissing in our democratic cornflakes is more than enough. The left is tearing itself apart over the burden of proof required to blame Russia for something that Russia most likely did, Brexit - which Russia actively wants - is off the front of the news which makes a hard exit more likely and Theresa May - who everyone recognises as a weak leader - is propped up because her opponent made a deeply unpopular and divisive statement. Add to that the lack of meaningful sanctions (so far) and they've already won.