But they can be gone.
The strength of the Enclave was that they were really the ONLY case of a vault working right. The USSA government had it's own vaults and they weren't designed to be any sort of screwed up experiments like the Vault-Tech vaults. So when they came out after the war, they had pre-war tech, the best scientists and their own small army. They reformed as the Enclave (lit. a distinct territorial, cultural, or social unit enclosed within or as if within foreign territory).
Fallout 2 ends with their main base being nuked. The AI at Raven Rock activated, summoned the survivors, and then they all got killed off in Fallout 3's ending. So all that's left at this point are rogue survivors and anyone left from the Chicago bases (hinted at in New Vegas).
So really their power is gone. Their main bases have been destroyed, their scientists killed off, their supplies of power armor and vertibirds tapped, etc...
They'll still be there, but as a reoccurring villain, they might be done. Fallout New Vegas might have handled the faction perfectly.