I have heard the word "existential" quite often, especially from the president, and quite honestly, was never sure of the definition. So, I looked it up. It means "grounded in existence or experience", "confirmable", "verifiable".
That makes sense as the word obviously has the word exist as its root.
While in Cuba, the President said that ISIL is not an existential threat. Tell that to the people of Paris, Belgium, or San Bernadino.
I'd say the threat from ISIL completely existential. The danger most certainly does exist.
When you understand his words, you understand his thought process. To say ISIL is not a threat, existential or otherwise is crazy. It is frightening that he continues to deny the danger.
Gladys Marsh