Well, technically they did. See... they destroyed the paper copies they printed out and had on their desk which would prove they were not 'tracking' terrorists, but political opponents and their supporters.
Without those 'printouts', no one can prove what phone numbers were selected, and what 'conversations' they had reconstructed from digital data.
Sure they did, wink wink. the computer that sent them to the printer still stores the numbers so by destroying the paper dont mean diddlie squat. Impeachment is the only sure way.