Sartre With Warheads

Here is a sentence I just now encountered in Yahoo News:

"If Israeli, U.S., or European intelligence gets proof that Iran has succeeded in developing nuclear weapons technology, then Israel will respond in a manner reflecting the existential threat posed by such a weapon," said Israeli Deputy Prime Minister Shaul Mofaz, speaking at a policy forum in Washington last week."

Is the word "existential" appropriate in this context?

Is everything that exists "existential?"