President Barack Obama's second pick to oversee US transportation security has withdrawn from consideration, the White House said.
Retired major general Robert Harding's nomination had raised questions about his past defense contract work that included providing interrogators in Iraq.
"It is with deep regret that I submit my withdrawal for nomination as the assistant secretary of DHS, Transportation Security Administration," he said in a statement.
Mr Harding added that he was pulling out to avoid having his defense contract work become a distraction for the Obama administration and the Department of Homeland Security (DHS).
Mr Harding was selected to lead the Transportation Security Administration just a few weeks ago, and officials had highlighted his three decades in the military, which included working as deputy to the Army's chief of intelligence.
"The president is disappointed in this outcome but remains confident in the solid team of professionals at TSA," said White House spokesman Nick Shapiro.
The withdrawal left the White House scrambling to find a nominee to lead the agency, which is responsible for screening passengers and luggage at US airports. Officials have described the post as one of the most important jobs that is still vacant more than a year into Mr Obama's presidency.
TSA has been under increasing pressure to boost and improve security in the wake of a Nigerian man's failed attempt to explode a bomb hidden in his underwear on a flight from Amsterdam to Detroit on Christmas Day last year.
Mr Obama's first pick for the TSA job, Erroll Southers, withdrew after concerns were raised about whether he had answered truthfully questions by senators about a reprimand he had received years ago. Republicans also questioned whether he would try to use the airport screening workforce.
During Mr Harding's Senate confirmation hearing earlier this week questions were raised about work at his old firm, Harding Security Associates, which he founded in 2003 and sold last year, though a key senator appeared satisfied with his answers.
Under scrutiny was a $6 million contract from the Defense Intelligence Agency to quickly provide interrogators and debriefers in Iraq. Mr Harding's firm won the deal but a few months later the contract was terminated by the military.
Subsequently, auditors raised questions about $2.4 million in payments and the two sides eventually reached a settlement in which Mr Harding's firm repaid $1.8 million to the government.
He told the Senate Homeland Security and Governmental Affairs Committee that one big part of the dispute was over about $800,000 in severance he paid to the 40 employees he had hired for the job. Under questioning by the committee, he said his interrogators were never implicated in reported cases of abuse of prisoners in Iraq.
That had apparently satisfied the top Republican on the panel, Senator Susan Collins, who had raised questions about the contract. She said Mr Harding had "adequately addressed my concerns regarding his former firm's contract."
Reuters