Most people know that polygraphs are notoriously unreliable and cannot be used in court, but that isn't the problem. Most of the time that they do not work well it is because of the sensitivity of the tests. Anything that triggers a person emotionally and/or makes them feel guilty could show up in the tests because of this kind of false positive error.
Imagine an employee is asked if they had ever leaked anything, but there was one time they thought that what they were doing was following a questionable order and merely thought about blowing the whistle. This could show up in a polygraph. But it's far more broad than that--many other things could evoke an emotional and guilty feeling depending on the person and situation, from voting once for a Democrat and not telling co-workers, to disliking some of Noem's or Trump's policies to strongly disagreeing with something their manager said that morning.
What happens next is the polygraph administrator will ask the employee what they were thinking about at the time or if there is anything to confess. The employee then might spill the beans like "Okay, I admit it. This time I didn't vote for Trump" or "One time I thought about blowing the whistle because I had to separate a child from their parents" or "I personally know a news reporter."
Doing these confessions can then cause the employee to pass the test in another attempt or they could simply continue to fail because of the sensitivity problem. Either way, this results in a lot of new information about the employee.
What do the managers, Noem, and/or Trump do with this information next now that they know? Does the employee get fired for "performance" reasons?
What would be the end result: storm troopers with no consciences? only completely loyal MAGAs?