The link attached is from 2013. If you recall, President Obama had a long, dramatic walk down the halls of the White House to arrive at his podium, with all networks live broadcasting. He then proceeded to tell the American people that a redline had been crossed, and it was undoubtedly Assad who was responsible for the attacks, and even though he had the authority to attack by himself (he didn't), he was going to put the question to congress.
This situation was the perfect example of why our Founders and the Constitution they penned were so explicit as to which branch had the power to declare war. Human's are fallible. We are driven by emotion, and the process of discussing and debating an issue as drastic as invading or attacking a sovereign nation is vital, as such a decision must not be made lightly or with haste. When bombs drop, people die. Sometimes those bombs kill bad people, and sometimes they kill good people.
It's easy to see people from other countries as "other" or the enemy, but anyone who has travelled to another country will tell you that it doesn't matter where you're from, we are all the same. We all share the same desires, we have the same problems, the same routines, etc. We are all human, and the decision to take the lives of other human beings is one that should not be made in the heat of the moment or without a great deal of discourse.
The current situation in Syria seems to be following the same path as in 2013. Assad has been largely winning the war, he has the backing of Russia, and President Trump had recently mentioned wanting to pull the troops illegally stationed in Syria out. Assad had no reason or motivation to do the one thing that would warrant U.S. involvement. Does that mean he didn't do it? Not necessarily. But that's why an investigation, and a debate need take place in this instance.
The Constitution is clear. This is an issue that must be handled by congress. From what I can tell, this was yet another attempt by rebel forces to push the U.S. into further involving themselves into the conflict, however my mind is open to all possibilities.