If you're a US citizen, the US government already knows enough about you from just your regular stream of activity that makes its way to them—your taxes, any times you've been arrested, etc. So—even disregarding stuff like Prism—they already have a baseline estimate for how trustworthy you are, without needing to do a background check. (Also, they can rely on other partial background checks you've passed in the past, if they have access to them. If you've ever worked with children, or gotten a NEXUS card, they already have all the information they need to determine whether you can work a government job.)

The same cannot be said of foreign citizens (even ones who are permanent residents); to the government's eyes, they're "opaque"—and even background checks run on them would only turn up what their homeland wants the US to turn up. (A background check that could turn up more, wouldn't really be a "background check" any more, but rather espionage, since they'd need to bypass the "public API" of the other government.)

>I’m convinced that the government doesn’t believe citizens are any more loyal or hard to bribe than other people, but insisting on citizenship would make it easier to charge us with particular crimes if the need arose

Hm.. I definitely feel it's easier to mitigate some risk by using US citizens. One of the goals is to limit possibility of foreign interference via these citizens. By using your own people, you can track their interactions with foreign entities via their trips outside of the US and their self documented contacts with foreign nationals. It'd be a lot harder to track these things when you hire someone from a different country because you're not going to have as meticulous records and all their friends and family are liable to be foreign nationals.

My non-citizen wife is a web designer for a minor department at the Smithsonian. They had to employ her through the non-profit, non-governmental side because the government side wouldn’t employ a non-citizen.

>I’m convinced that the government doesn’t believe citizens are any more loyal or hard to bribe than other people

Seriously? While they have to plan for an inside threat, do you really think that they don't view their own citizens as being more reliable than foreign nationals?

>I’m convinced that the government doesn’t believe citizens are any more loyal or hard to bribe than other people, but insisting on citizenship would make it easier to charge us with particular crimes if the need arose.

It is not always about the security side. There are certain requirements to employ US citizens based on the funding source. The charitable reasoning is ensuring the program can continue to run even if are at war.

Requiring U.S. citizens denies adversaries the ability to use their own without first having to put them through immigration and naturalization in the U.S. That's not nothing. Sure, adversaries can also recruit Americans, but that's harder than recruiting their own citizens.

Does it prevent espionage by Americans? No. But it does make espionage by foreign adversaries at least a bit harder.

I'd say requiring own citizens also makes it possible to play eenie meenie among a pool of candidates, to minimize the chance of spies slipping in.

They leave cellphones in lockers because they have cameras. There are corporations that have similar places. I’m sure Apple doesn’t allow cellphones in certain rooms with prototypes.