I'm trying to understand how to parse the がってんなら in this sentence (it's from Tales of Vesperia, in case anyone's curious):
This is how it's translated in the English version of the game:
Haven't you already seen what
the empire's capable of several
times on this trip already?
The second part of the sentence is easy enough, but I just can't wrap my head around the first part. Is it short for 帝国があっているなら or something? And what would that translate to literally? Is there some bit that's omitted that I should be able to infer from context?