To what extent, if any, has the Turkish agreement with the U.S. in creating a ‘safe zone’ been influenced by back-home politics in Ankara?
First, I question how much of a “Turkish agreement with the U.S.” there actually is on creating a safe zone. The U.S. has been explicit that it is not committed to this. As for Turkey, there can be little doubt that domestic politics weigh heavily on Turkish policy towards not only the safe zone in Syria, but also towards the Islamic State. A principal domestic factor is the Kurdish question, which is the primary lens through which the Turkish government views crises and conflicts in Syria and Iraq, which have their own significant Kurdish communities. But at present it is electoral calculations that drive Turkish policy on these issues: the recent parliamentary elections left the ruling AKP in a weakened position and dependent on forming a coalition government which it does not wish to do, so it appears to be escalating the conflict with the PKK, since it has given up on the Kurdish vote, in order to harness both nationalist and Islamist sentiment to win back some of the votes it lost to other parties.
As Turkey started air strikes against ISIS, it also attacked the PKK in Northern Iraq and the YPG has claimed it has been struck. What key factors must be achieved to ensure the Kurdish U.S. allies are protected and their alliance is maintained?
The U.S. faces a difficult set of choices. On one hand it continues to regard the PKK as a terrorist organization, but has indirectly assisted its sister organization in Syria, the PYD, in its fight against the Islamic State. The U.S. also assists the Kurdish Regional Government (KRG) in Iraqi Kurdistan, which has bad relations with the PKK but good ones with Turkey. On the other hand, the U.S. has been careful not to endorse calls by the KRG for full independence of Iraqi Kurdistan, and not to commit itself to Kurdish autonomy in Syria. So U.S.-Kurdish relations are complex. But the U.S.-German decision to withdraw the Patriot air defence missiles currently deployed in Turkey under a NATO mandate, which was done in consultation with Turkey, suggests that Turkey's NATO partners are uncomfortable at seeming to stand by the resumption of armed hostilities by the Turkish armed forces against the PKK, whether inside Turkey or across the border in northern Iraq. So this may be an initial attempt to limit how far Turkey escalates its new conflict with the Kurds.
How should (or can) the U.S. best maneuver the current agreement to make headway, not only against ISIS but in to best position itself in dealing with the varied situations in the Middle East?
I am not clear what is meant by this question. The only real agreement between the U.S. and Turkey at the moment focuses on U.S. use of the Turkish Incirlik air base to launch attacks on ISIS. This has limited scope and impact and does not represent a dramatic or strategic transformation of U.S. ability to act in the region, which is already considerable thanks to its use of fleets in the Mediterranean and the Gulf and to the use of bases in GCC countries. Conversely, it is evident that the agreement over Incirlik has not given the U.S. any extra influence with the Turkish government, which is not as seriously committed to the fight against ISIS as it is to fighting the PKK and has resumed its pressure for a safe zone or no-fly zone in Syria.