The S-400 anti-aircraft missile system have arrived at the Hmeimim airbase
For use against who? Daesh don't have aircraft, SFAIK; I'm not sure anybody local other than the Syrian regime and 'fellow' international forces against terrorism have aircraft. And shooting down a Turkish aircraft (across/on the border) isn't going to help, and the possibility of the warheads with 120-400km range 'doing an MH17' is going to cause tension. Never mind if something like that happens.
Haven't you read the last several pages? It's because Turkey shot down a Russian jet and now the Russians are putting that there because they're threatening (and actually have a right to) to shoot down any Turkish aircraft that does do that.
Of course though, both sides ramping up the rhetoric and not backing down isn't helping.
That's the gist of the "And [it] isn't going to help..." bit. Either it is an empty threat and doesn't mean anything or its a non-empty threat that will be accompanied by more 'border-scrapers' from the Russians which Turkey's not likely to back down from, merely station counter-counter-measures of its own, etc.
And I tend towards the latter, to be honest. Then
at best it ends up as two one-legged men in an arse-kicking contest
1. I've got a friend who honestly predicts that (without de-escalation) there'll eventually be tactical nukes involved at some point... Beyond my own vision, but there's plenty of ground that can be covered between those positions, even without considering the dragging in of the other countries expressing interests in that area...
So let it be an empty threat. "We haz
cheezburgers bigger gunz", perhaps. Speaking moderately loudly, holding their big stick, but also happening to no longer cruise their Declasse Tornado Soft-Tops along the borders of the other gang's neighbourhood quite so flagrantly.
(But what do I know? The mindset of the Russian and the Turk aren't my speciality.)
1 Ok, so one of the men is Big Ivan and the other is only Moderately Large Mustafa
2, but the bigger the man the bigger the targeted arse.
2 As in Ataturk, lest anyone think I'm going the way of an irreverent toponym.