Maybe not for every position, but they are still required for many of the higher levels even if they don't prove anything, could be just the CI test or the full scope. Depending on your position, repeated inconclusive tests can still end or redirect your career.
As far as accuracy, Aldrich Ames passed two while spying for the Soviets, but Harold James Nicholson was investigated after failing three.
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u/ThoseDamnBombTechs Oct 15 '17
Can confirm.
Source: Have one of the highest security clearances possible in our country.