Late last year, US forces announced an offensive against Raqqa, the de facto capital of ISIS territory, aiming to take over the city with a small US force and a lot of embedded Kurdish YPG fighters. Months later, the Kurds haven’t gotten far, taking a bit of the far-north of the province.
ISIS’ position in Raqqa is far from secure though, with Turkey talking up sending their own invasion force to Raqqa soon, and the Syrian military also trying to push its way into Raqqa Province from the south. That’s a lot of enemies for ISIS to fight all at once.
On the other hand, these forces don’t get along with one another either, so as they all race toward Raqqa, there is a very real possibility that the different groups will run into one another first, and decide that’s the fight they want instead. That potentially gives ISIS an opportunity to take advantage.
This has already been seen in limited fashion in al-Bab, a smaller ISIS city, where Turkish and Syrian forces ended up getting into a brief fight before Russia managed to break it up. Turkey has been very open about their hostility toward the Kurds as well, which is likely to be an even bigger fight.