There is a lot of talk in Western Media that ISIS will be able to re-establish itself in Syria if the US pullout. Of course their argument completely overlooks the fact that Assad and Russia have also cleared ISIS from large areas in Syria, including Deiir Ezzor where they had a large presence, and presumably will continue doing so as fast as they can.
So what is the actual report card? Which side has been most effective at eradicating ISIS and which one is best positioned to continue the job and why?
I don't buy that argument at all. The US and the SDF/YPG made incredible gains against ISIS, seizing Raqqa and the area around Tabka airbase, when the race was on against Assadist forces. However after the behind-the-scenes deal was struck regarding the de-facto partition of Syria along the Euphrates (with some minor exceptions), and ISIS was chased into a small, geographically less relevant area, the US-backed offensive slowed to a crawl. While the Syrian government forces and allies actively and aggressively went after any ISIS-held territories, leaving only small roving bands in the desert, from where I sit it appears that the US and the SDF/YPG have intentionally allowed ISIS to retain a small patch of territory. Given that the US has no legal justification for it's presence in Syria, allowing ISIS to remain on the map is a good way to continue claiming that the US is there to "fight ISIS", even though it's also openly being said that the US is there to counteract Iranian influence.
On the subject of report cards, I don't think it particularly matters. When ISIS became the focus of their efforts each side was able to eliminate them rapidly and fairly effectively, albeit with significant foreign support (the US backing the SDF/YPG, Russia/Iran backing the Syrian government). Either side is fully capable of crushing the last ISIS foothold rapidly and decisively. Assad is prevented from doing so because the enclave is on the east side of the Euphrates. What prevents the SDF/YPG? How little time did it take to seize Raqqa and how relatively easily were great resources brought to bear on the problem? How long since then have the Kurds and their backers been butting heads with a much smaller ISIS in the south-east? In my opinion, therein lies the key to understanding this situation, and any claims regarding the US being some sort of guarantor to ISIS not re-emerging should be disregarded as blatant lies.
Or, if one is in a more cynical mood, interpreted to the effect that the US might go back to pumping weapons into questionable hands in Syria, should that be the only way to prevent a complete victory of a pro-Iranian Assad. In which case the US withdrawal could indeed lead to a resurgent ISIS, not because the US was holding them back, but because US actions would contribute to their resurgence. Though honestly, I don't think that's a likely outcome. With a US withdrawal, a major Turkish operation in the north, we would probably see a concentrated effort on the part of Syrians, Iranians, and even the Iraqis (sealing their side of the border), to finish off the last ISIS pocket with extreme prejudice.
