Less than a month after he came under stinging criticism from whistleblowers testifying before Congress, the chief of the Transportation Security Administration’s key security division has been replaced.

TSA Administrator Peter V. Neffenger defended security chief Kelly Hoggan in his own testimony on Capitol Hill on May 12. On Monday, he announced in a memo to TSA staff that Hoggan had been replaced.

Though TSA is best known for the blue-shirted security officers that staff its airport checkpoints, the unseen side of the 60,000 member agency is a vast intelligence network that interacts with other federal intelligence agencies in an effort to protect the nation’s transportation system.

Neffenger's predecessor as administrator, former FBI official John S. Pistole, set out to transform the TSA from a front-line agency known for its defense of airports into an intelligence-gathering organization that identified and acted on terrorist threats.

 With operatives overseas and on the ground in major American cities, the TSA coordinates real-time intelligence information in a vast center in Northern Virginia that tracks suspected terrorists around the world and evaluates incidents here and abroad.

Kelly Hoggan, former head of security for the U.S. Transportation Security Administration (TSA), is seen in an undated picture from the Transportation Security Administration. Hoggan was removed from his position on May 23, 2016. (Handout/Reuters)

The criticism of Hoggan by three whistleblowers who testified before the House Committee on Oversight and Government Reform in April focused on the fact that he had no prior experience in the intelligence arena, that he played a role in punitive reassignments of whistleblowers and that he received $90,000 in bonus pay for his TSA work.

Neffenger defended Hoggan before the same committee on May 12.

“I do not currently have a plan to remove Mr. Hoggan,” said Neffenger, who became TSA administrator in July, after the allegations had been lodged against Hoggan. “I have not seen any direct misconduct on the part of Mr. Hoggan in the time I have been here.”

In the staff memo on Monday, Neffenger named his deputy assistant administrator, Darby LaJoye, as Hoggan’s acting replacement. He also elevated Rod Allison, who has headed the Federal Marshall Service, as his deputy chief of operations.

“These adjustments will enable more focused leadership and screening operations at critical airports in the national transportation system,” Neffenger said in the staff memo.

Here are four reasons so many flyers are getting stuck in long security lines at the airport. (Claritza Jimenez,Dani Johnson/The Washington Post)

At the April oversight committee hearing, the lawmakers heard from whistleblower Mark Livingston that “The refusal to address or to hold senior leaders accountable is paralyzing this agency.”

He told the committee that when he raised concerns, his supervisors reduced his pay by two grades and “sought to make an example of me.”

Monday night, Livingston said the replacement of Hoggan as assistant administrator for security operations did not resolve that issue. He said that other top leadership who approved excessive bonus payments and directed punitive reassignments to distant locations “need to be held to the same accounting.”

“I also kept telling Congress that character assassination was an Olympic sport at TSA, Livingston said. “Once you told the truth, they would do any and everything to destroy you.”

He said that he and the other two whistle blowers — Andrew Rhoades, an assistant director in the Office of Security Operations, and Jay Brainard, a TSA security director in Kansas — had not been given an opportunity to share their concerns with Neffenger.

“Neffenger promised to have an open-door policy for retaliation cases, but he has not even spoken to the three whistleblowers or the others who might have requested to see him,” Livingston said. “He cannot fix the airports if he can fix the most obvious management issues that Congress and whistleblowers show him.”