Although where ordinarily stands for an entire preposition phrase—the store where I buy my beer is equivalent to the store at which I buy my beer—the implied preposition is often supplemented with an express preposition. Because the 'default' interpretation of where is that it designates a static location, the supplemental preposition is almost obligatory when where designates the origin or a goal of some motion. For instance,
Where I am designates my present location, but
Where I am from adds the preposition from to indicate that where designates my origin, not my location.
That's probably what's going on in the President's speech. Furthermore, I think it very likely that it this was originally something like where the chemical attack was launched from, which is the natural way of expressing this, and somebody with a typically legal/bureaucratic sensitivity to language (that's an oxymoron, in case you missed it) pied-piped the preposition to the front without adjusting.
Supplemental prepositions are not limited to situations like this: they are also used with ordinary locatives. This is very common in casual speech, and usually deprecated in formal speech—
Where are you at on the 17th?
is probably not something you should put in a business inquiry. But sometimes the supplemental preposition provides a particular idomatic sense. Back in the 60s, for instance, the phrase where it's at was a common designation for clubs and other venues regarded as especially fashionable:
Come on, come on, let me show you where it's at
The name of the place is I like it like that.
—'I Like It Like That', Chris Kenner