It's interesting that this happened around the same time the Nikki Haley made a statement to the effect that regime change in Syria is no longer a priority. And not to mention the Leader of the Free World initially seems to blame these attacks on Obama, instead of the people who actually carried the out the attack. It's possible Assad and Putin are emboldened by Trump administration's position on Syria. It's a way to test the United States. If the U.S. responds, they adjust their strategy accordingly. If the U.S. doesn't respond - which is what they're betting on - then they know they have a free hand to do whatever they want. Geopolitics 101. Or it is to prompt the U.S. in an even more active role in Syria, to come to the aid of Idlib. Propaganda warfare 101.
When you think about it, Assad had no good reason to gas these people. He's effectively won the civil war and this doesn't make his victory any greater. This could be specifically aimed at testing Trump & Co. and how they will react to provocation by a Russian proxy.
King Abdullah made it very clear today that he views the Israel/Palestine issue as the root cause of the disfunction in the region and that needs to be the priority. You could almost read between the lines that he was looking for some help from someone other than Jared Kuchner.