What if someone is absolutely perfectly innocent, but refuses on the principle of the intrusion?
They serve at the whim of the President and should want the leakers to be identified, if they have nothing to hide, they have nothing to fear. I once held a job where taking a polygraph was a condition of obtaining the job and retaining it. Those with access to such classified information paid by the tax payers and working for the President should be held to the same standards. If their principles are so strong they refuse to take it, they're free to look for a different job outside of the White House. No one stopping them. I'm betting everyone of the Obama holdouts would refuse to take it since they all are doing what they can to undermine the President in some way or another, a good way to clean house.
Now, Kim would just kill two people every time there was a leak and when the *** stopped, he would know he had the leaker.