On one hand, this should not come as a surprise. Turkey is a member of NATO, and the mutual-defense agreement gives Turkey the option of calling for assistance in case of attack — and Syria has already launched missiles at Turkey during this conflict.  The troops in question will be manning these defensive systems rather than taking part in an offensive strategic deployment, especially with only 400 US troops in question.

Still, if Syria’s Bashar al-Assad gets desperate enough, the threat of escalation is pretty clear:

The United States and Germany are sending Patriot missiles and troops to the Turkish border, a warning to Syria’s besieged President Bashar al-Assad.

The surface-to-air interceptors would be “dealing with threats that come out of Syria,” said U.S. Defense Secretary Leon Panetta. Threats would include Syrian strikes inside Turkey and fighting between the government and rebels that extends into Turkey.

Errant Syrian artillery shells struck the Turkish border town of Akcakale and killed five Turkish civilians in October.

“We can’t spend a lot of time worrying about whether that pisses off Syria,” said Panetta after signing the order Friday. He spoke after arriving Friday at Turkey’s Incirlik Air Base, a U.S. Air Force installation about 80 miles from Syria’s border.

I think “piss[ing] off” Assad is part of the point, and even more so, intimidating Assad into bailing out of Syria altogether.  The latest fear is that the Alawite clan will collapse back into the mountains, turning Syria into a replay of Lebanon a generation ago, with endless civil wars and territorial fights.  Failing that, Assad might be tempted to draw Turkey into the fight as a way of muddying the waters, which is why the US and Germany have decided to send this message.

Will this move by NATO convince Assad to give up and start shopping for dachas near Moscow?  Probably not, but it might keep him from escalating the fight in an attempt to draw support from his allies, which have been consistently at arms’ length in this fight.  But if it doesn’t, the US and German presence might end up dragging NATO into a fight that it has also consistently avoided engaging, and that might put us back in the same position in which we find ourselves in Libya and Egypt — with Western power (military and diplomatic) serving to put radicals in power in replacement of despots.