Yes your president clumsily gave the regime Assad the false confidence it could push harder.
Investigate?
Why do you not read the actual news reporting and look at some maps before repeating extremely stupid conspiracy thinking.
So you think DAESH which has no presence and is hundreds of kilometers away separated by the territory controlled by the Regime Assad some how got the highly unstable, dangerous, complex Sarin to the enclave controlled by their sworn enemies, an Nusra? Oh that makes great sense… No in fact it is an idiotic proposition.
So you think An Nusra is the logical explanation because… it makes sense that the dangerous, unstable Sarin would be able to be quickly transported to the exact spot where the Regime Assad warplanes struck, and set off the gas Sarin in the exact timing of airstrikes and in the EXACT place? God must be guiding them to have this specific knowledge so magically.
What magical expertise an Nusra has to know where and when precisely a warplane will strike!!!
Of course even the Regime Assad is not claiming anything but that their warplane " accidentally " struck a reserve that an Nusra had in place, by coincidence… An illogical claim as your own Pentagon has shown the strike crater to be in the middle of a road, not in a building storage.
Or one can say that the Regime Assad with the known ability to produce the Sarin precurosors (it is an instable acidic chemical that can not long be stored in its killer form) and with the known ability to deliver it via the warplanes, and with the known predeliction to use the air bombing terror weapons - like the chlorine gas, like the barrel bombs, like other chemical attacks got over-encouraged by the stupid, loose, uncareful statements of your government and your President and decided to test if they could push harder.
Since the Syrian civil war started from exactly this terror oriented behavior of pushing to far by the Regime Assad, in the ordering of terrorist attacks against the peaceful civilian demonstrators that led a good portion of his own military to revolt, it is not in any way surprising to see the Regime make this kind of error.
Or you can come up with ignorant and illogical conspiracy stories to excuse the incompetence of your goverment discourse in the past months.