Sure, a system could be designed where the “master key that unlocks everything” is distributed - that makes the problem of the attacker who wants to get his hands on that key slightly harder, because now he has to compromise three systems instead of one, but that doesn’t change the fundamental risk, which is that he can do that in the first place. Remember, you’re talking about one piece (or three pieces) of information which can be used to decode every single secret in the United States - this isn’t limited by technical feasibility, this is the explicit end goal that you’re asking for. If Russian hackers got a hold of it undetected, they could decrypt everything for a very long time. Even if it were revealed that it were compromised, everything that was encrypted using the old key would have to be re-encrypted somehow, and the old copies destroyed somehow.