Thiose little words make ...

.
... a lot of difference:

“Had this information been reported, properly adjudicated and acted upon, [Aaron] Alexis’s authorization to access secure facilities and information would have been revoked,” the report said — and the shooting might have been prevented.

'Might' have been prevented.

Cooke goes on to note that had all of the president's gun control measures gone into effect it would have made no difference in the outcome at the Navy yard.

But you already knew that, didn't you?!

pm