The withdrawal late Friday of Maj. Gen. Robert Harding to head the Transportation Security Administration leaves the Obama administration scrambling to fill what it has called its most-important vacancy.
Gen. Harding, a 33-year veteran of military intelligence, withdrew his nomination to head the TSA, which oversees security at U.S. airports, in the wake of grilling by senators over his security firm's business providing interrogators to the Pentagon in Iraq.
"I feel that the distractions caused by my work as a defense contractor would not be good for this Administration nor for the Department of Homeland Security," he said in a statement released by the White House.
The TSA has been without a full-time boss for more than a year, even as attempted terrorist attacks, such as the Christmas Day underwear bomber, have highlighted the ongoing vulnerability of commercial aviation.
Gen. Harding was the second to withdraw his nomination to the post under theObama administration; Erroll Southers pulled out in January after coming under fire from Republican lawmakers. A White House spokesman declined to say when the administration would nominate another candidate to head the TSA.
Former security officials from the Federal Aviation Administration and the TSA said they aren't aware of any particular names that might be on the administration's short list.
Billie Vincent, a former director of security at the FAA, highlighted the importance of filling the top spot at the TSA, especially since aviation officials in other countries "look to the U.S. for leadership" on aviation security, he said.
The next pick must be somebody "who understands intelligence, and who can stand up to the airlines" that often push back against what are seen in the industry as onerous security measures, Mr. Vincent said.
The Obama administration's difficulty in filling the top spot at the TSA is part of a broader problem of securing Senate approval for many key nominees. Mr. Obama made 15 recess appointments on Saturday, as Congress began a two-week break, sidestepping what the White House called "an unprecedented level of obstruction in the Senate." The appointments included those for key figures at the Departments of Treasury and Commerce, and the National Labor Relations Board.
Gen. Hardings's withdrawal leaves the TSA without a boss at a time when aviation security has soared to the top of the agenda at the Department of Homeland Security, in the wake of the failed Christmas Day bomb attackon a Detroit-bound airliner.
DHS Secretary Janet Napolitano has met with aviation-security officials from Latin America, Europe and Asia this year to figure out how to bolster information-sharing among countries and improve security screening at airports around the world. Failings on both those fronts were evident in the attempt by Umar Farouk Abdulmutallab to detonate a bomb hidden in his underwear on Dec. 25.
Among the challenges facing the next TSA chief will be beefing up airport screeners' ability to detect dangerous materials. The TSA hopes to roll out a new generation of enhanced screening machines at a cost of more than $2 billion.
But a recent report by the Government Accountability Office found that the new machines, known as "advanced imaging technology," may not have been able to detect the explosive used in the Christmas Day attempted attack. Additionally, the GAO found that other machines designed to detect explosives had not been fully tested by the TSA before being deployed.
The next TSA head will also have to negotiate over collective-bargaining rights for security screeners, an issue that ensnared both of the administration's previous nominees. Republican lawmakers worry that granting such rights to screeners could hamstring the TSA's ability to shift security workers among different airports to meet new threats.