Turkish forces have entered Syria and while engaging with ISIS, they have also engaged with the Kurds. A major confrontation nearly erupted between UF Special Forces and Turkish fighters, but this was averted. Instead, the US promised to convince its Kurdish allies to withdraw east of the Euphrates River. This did not stop the Turks from continuing to engage the SDF, led by the Kurds, and it may not end any time soon.
The issue for the Turks is that they fear an empowered Kurdish force would embolden the Kurds with Turkey and also provide a safe haven for the PKK. The US is allied with both the Kurds in Syria and with Turkey and it is therefore becoming clear to US foreign policy officials that some sort of serious agreement must be made. The Turks have shown the seriousness of their claims and the US does not want to lose Turkey. Since relations with Turkey are already sour, a serious accommodation must be made.
The Turkish intervention was primarily aimed at stopping a link-up of Kurdish forces between the Afrin and Kobani cantons. Therefore, the Turkish intervention was aimed at preventing the formation of a Kurdish state with legitimate claims to power in Northern Syria. The US is ready to adapt to this new reality, but it must find a new role for the SDF forces that it has been training. That new role will be a minor Kurdish state which will be active in campaigns towards Raqqah, the ISIS capital. Since the Kurdish march westwards has been effectively halted, the march southward to defeat ISIS must be pushed.
The Turks, however, will not want this either and will make their own attempts at Raqqah. Part of this will be subverting Kurdish authority in their main regions, by encroaching into towns like Kobani (as they have done recently) and by encouraging Arab tribes in the Tel Abyad region between Kobani and Cizre to revolt. Meanwhile, the Turks will attempt to liberate al-Bab and from there launch loyal forces towards Taqbah and the regions around Lake Assad. If this fails, they may even pursue an offensive from Tel Abyad.
Please see a detailed ethnographic map of Syria to understand why an offensive through Tel Abyad is possible:
All of this will create a competition between the Kurds and Turkey for defeating ISIS. The US will find itself in a difficult situation as their plans to accommodate the Kurds for an advance on Raqqah will be foiled. In the end, they will choose whichever side has the better chance of taking the ISIS stronghold. These competing campaigns will not be finished by the end of this month, but they will begin by then.