I'm not sure what's your background whether you have any political or diplomatic knowledge and understand the language, that's one, then what knowledge do you have about the entire conflict? Do you know from where ISIS came into Syria? Do you have any idea how the 'US saw them growing'? Did you hear why that US increase their presence in Iraq to fight ISIS?

Unless you know that and have proper background you can't pick on the literal meaning of the words at the moment given without understanding how did the US see them growing when they had thousands of their troops in the same place where ISIS came from and how they never interfered to stop them in Iraq when their sole mission there was to stop them from growing, on the contrary they facilitated the movement of thousands of ISIS fighters in brand new Toyota 4x4 machine-gun mounted pickups, and how the US turned a blind eye to ISIS atrocities against the Iraqi Yazidis and Kurds just to use them in the future to pressure Assad, then who will stop them if Assad accepted to negotiate and how will the US stop them at that time?

Here's a background if you're interested in understanding the geopolitics of the Levant and Iraq in regard to the creation and growing of ISIS, and keep in mind that Hillary Clinton before a Congressional Hearing admitted that the US created al-Qaeda before in Afghanistan to use them against the Soviets, and pay close attention to the date this was published: https://www.syrianews.cc/isis-the-bombshell-interview-to-impeach-obama/