President Obama's choice to lead the agency that guards United States airports abruptly withdrew his nomination on Friday night amid questions about his work as a defense contractor, the second time the White House has lost a nominee for the critical security post.
Maj. Gen. Robert A. Harding, a retired Army intelligence officer, was selected to take over the Transportation Security Administration, or T.S.A., just two and a half weeks ago, following the withdrawal of Mr. Obama's first pick under fire.
No third choice was announced, and the back-to-back failed nominations mean that the job is likely to remain unfilled for months to come.
