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Three months after the attempted bombing of a U.S. airliner on Christmas Day, the Transportation Security Administration, guardian of the U.S. aviation system, remains leaderless.

President Obama's first nominee for the agency's top job, former FBI agent Errol Southers, withdrew in January after admitting he'd once used a federal database to name-check his estranged wife's new boyfriend.

The president's second nominee, former Army Major Gen. Robert Harding, withdrew last week amid questions about his lucrative work as a Defense Department contractor.

"The longer it takes to get a permanent TSA head, the longer it will take to make those needed reforms," said Steve Lott, a spokesman for the International Air Transport Association. "We need someone that's going to come in with a fresh new strategy, that can improve security, that can tackle some of the new and emerging threats and can manage the thousands of screeners, the large workforce out there."

The morale of the nation's 40,000 airport screeners is considered critical to the success of the agency's counterterrorism mission.

A spokesman for Homeland Security Secretary Janet Napolitano, to whom the TSA administrator reports, told Fox News, "TSA's senior career leadership team has decades of experience in transportation security and is working every day to increase our nation's security. Secretary Napolitano has full confidence in Acting [TSA]Administrator Gale Rossides and her dedicated team's ability to fulfill TSA's important mission…"

But experts countered that TSA suffers from interagency clashes over turf and resources and that the agency can't make bold, forward-leaning moves to meet today's threats.

"We just had a terrible incident in Moscow," said Tom Blank, a former TSA deputy administrator, referring to the subway bombings there. "There has been concern for some time that TSA needs a broader initiative to secure America's subway systems. Without a permanent leader, something large, with far-reaching implications, isn't really going to be taken on."

The Obama administration has not yet named its third nominee. But many analysts believe that, in order to avoid another fiasco, the nominee should come from within the ranks of the TSA itself.