I've been around long enough to have made a few observations about institutions. Number 1 is that when they consist of transients and lifers, like colleges (students vs. faculty) or govt agencies (political nominees vs. civil servants), the lifers end up running the show. Number 2 is that regulatory organizations get "captured" by those they are to monitor and often end up putting the interests of the regulated above those who are to be protected from them. The latter is in part influenced by the fact that the monitored organizations are in a position to reward their regulators while they serve (which is illegal) or afterwards (which usually is not illegal, and is also common). Number 3 is that they have political views and interests of their own independent of those who found or support them, and tend to react to events in a ways that maximizes their power and influence. Nothing controversial so far, right?
OK, now apply these ideas to the US Department of State and you must conclude 1) politicians will not be able to control it very well, 2) The same department is likely to be more sympathetic to the needs of foreign govts than to our own. 3) Its institutional self-interest isn't always allied with those of the rest of the US govt.
Hmm, does it follow that we can't trust our State Department?
That's probably a bit strong. But as a minimum it means that we must keep a close eye on it, and that is borne out by experience. For instance we do know that there have been Communists in the State Department since way back in FDR's time, and if any group has interests contrary to those of the US, that's the one. And we've seen some disconcerting behavior for some time recently, as Joe Mowbray has documented in many places. Here is his latest piece, and a forthcoming book.