That's fine and dandy, a good word, although in context it's not being used correctly.

Trump is NOT an "existential threat to decency" as Biden has said. I'd say Biden is an "existential threat" to a proper and correct definition of "senility" or "intelligence".

And, despite what Bernie Sanders and Greta Thunberg insist, climate change is not an "existential crisis". Sanders' views are the genesis of an "existential crisis" insofar as America's future is concerned and Thunberg is a prime example of a "mistake of existential proportions" as to the proper way to raise an emotionally balanced and free thinking child.