Former national security adviser Michael Flynn never received the security clearance required for the job, NBC reported Monday. "When he became national security adviser, Flynn was required to obtain a new White House security clearance under the auspices of the CIA, which vets national security appointees," NBC reported. "That clearance was never granted before he was pushed out of the job, one official with knowledge of the matter said." Flynn left the Trump administration in February, after it was revealed that he lied to Vice President Mike Pence about communications with a Russian ambassador. Former President Barack Obama warned Trump about Flynn two days after Trump's election, NBC previously reported, and during a sit-down meeting, Obama personally cautioned Trump against hiring Flynn to the national-security post.