Directly attacking the health of US personal would be a hugely provocative act. I’m not saying the Russians wouldn’t do it. There are reports that they paid out bounties in Afghanistan to attack US troops. But launching a campaign to enfeeble the intellect of future high level state department officials in this manner doesn’t make much sense. If you tried this kind of attack on a large scale and targeted a significant number of personnel, you would surely get caught which would lead to severe consequences. If you did it on a small scale that you might get away with, it would still be a risky and expensive undertaking and you’d only end up hurting a small fraction of one percent of possible future leaders. The cost benefit analysis doesn’t make sense to me.
We obviously don’t have enough information to really know what’s going on here but I do thinking some possibilities that don’t make very much sense can be excluded.
Probably a very low percentage of low level staff today will be high level staff 15 years forward - especially if you microwaving them. If that were the adversary's intention then I would expect hundreds or thousands of our staff to be suffering. As is, it looks like only a few people spread across decades. Malfunctioning of a microwave power source is the only thing that makes sense to me.