The CIA employees MUST take a polygraph if requested. I recall this from back when the Plame situation arose. That would be a good start in purging the traitors.
But as Hillary infamously said (after her rape client passed his lie detector test) ‘it forever ruined my faith in lie detectors’. They don’t always out the liars.
Part of the periodic polygraph tests they take to maintain their security clearances, should include questions about how they feel about Islam. Pro-Islamics should be tossed out. Given what we've heard about Brennan, the CIA is likely to be heavily infested with Muslim Brotherhood sympathizers.
One problem with some of them though...polygraphs operate on the principle that since the subjects know that it is wrong to lie, physical changes occur. Any who are followers of Islam to the degree that they fully believe in the rightness of taqiyya may be able to beat the tests, as they are certain that it is never wrong to lie to the Infidel on behalf of Islam. A minority, for sure, but a dangerous one.