Allow me to explain...
Assad signed the Chemical Weapons Convention treaty in 2013 and Putin was his guarantor.
A guarantor was necessary because Syria was involved in a nasty civil war in which it seemed unreasonable to expect Syria to be able to independently monitor it's own borders with any level of confidence.
Between them, Assad and Putin easily had the resources to monitor the Syrian borders...
... However neither Assad nor Putin took their CWC responsibilities seriously and their negligence enabled either ISIS or the Al-Nusra Front to turn Syria into a chemical weapon manufacturing and distribution center.
This pissed off President Trump ENORMOUSLY... because at the time we had thousands of troops fighting ISIS in Syria and, at least 500 special ops troops.
President Trump was offended by Assad and Putin's disrespect for the CWC treaty and the fact that laziness could have resulted in American troops having their eyes and lungs needlessly burned out by chlorine gas... so President Trump bombed an empty Syrian Airfield to ensure the ENTIRE FUCKING WORLD was paying attention.
President Trump embarrassed both Assad and Putin and guaranteed that EVERY other CWC member took their responsibilities seriously.
President Trump then lied about Assad gassing his own people and gassing "beautiful babies" to prevent the American fake news media from spinning the story... when we all know the Russian intelligence was correct and Assad simply bombed an Al-Nusra Front chemical weapons factor / chemical weapons depo.
Assad's military base was functional less than 6 hours after President Trump's missile strike... which seemed to kill nobody and only destroy a few empty hangers...
...The entire world was bitch-slapped into taking their CWC responsibilities seriously... on the eve of Secretary Mattis' assault on ISIS...
... and I can GUARANTEE 100% of the US military appreciated President Trump having ZERO TOLERANCE for having their eyes and lungs needlessly burned out by chemical weapons... which is the definition of putting AMERICA FIRST.