National security?
Thats what guided your policy from the get go in Syria?
Turkey, instead of playing its usual role of mediator, made a concious choice to actively support the rebels in order to overthrow the soveireign government (whether you like that gov. or not) of a neighbour country.
I hardly see how that helps with the national security thing. Especially since Turkey is now exposed to multiple more security threats on its southern border. You have batshit crazy Salafist Jihadis, and then you have Kurish YPG that have taken a lot of control in much of northeastern Syria.
Not to mention that you have effectively turned Syria into an enemy state. Do keep in mind that the Syrian government is still recognized as the sovereign government of Syria. Unless Turkey manages to militarilly overthrow it in long term but that will require resources, long term commitment/occupation and will carry dangers. Especially since Syria is a bordering country.
Turkey can potentially find itself in a debacle, like US in Iraq, should it decide to go further and increase its military precense in Syria.
This Suleiman tomb excuse can be genuine but it can also be a pretext for wider involvement.
Sorry but Turkish policy in Syria so far has made very little sense, if any, from the point of "national security".