Stephen Colbert quizzed the leading diplomat about whether Trump's critique of Obama's Syria policy is the right one.
The Pentagon has denied responsibility for the attack.
The U.N.'s finding has vindicated the U.S. and its allies.
The images of the four-year-old injured in an air strike shocked the world one year ago.
An internal memo said the U.S. must threaten military strikes to deter Assad.
It is hoped that the factions can form a united opposition ahead of January peace talks with the government.
"If the international community had instituted the no-fly zone, Aleppo would be free today."
Assad flew to Moscow on Tuesday evening to thank Putin personally for his military support.
Bringing Russia in to bolster Assad's regime could risk Iran's strategic command of the situation in Syria.
Though Putin may look like he's in control in Syria, the intervention is likely to end badly for him.
Adel al-Jubeir said that Assad must either leave voluntarily or face being forced to step down.
The disgraced former CIA director and army general was there to offer his views on the Mideast.
Assad knows the rebels' backers are not interested in a decisive rebel victory.