The Department of Homeland Security is suffering from a leadership void as the nation's youngest Cabinet-level agency faces a host of growing pains.

President Obama has yet to pick a replacement for Janet Napolitano, who said three months ago she would step down as secretary in September. Fifteen other top jobs are vacant. Employee morale is alarmingly low as the debate over comprehensive immigration reform drags on, and airport security remains a sore point with both the public and the DHS. Deadly attacks in Boston and Washington have the nation — and agency — on high alert.

Ten years ago, a recommendation from the 9/11 Commission led to the creation of the department. Since its inception, DHS has been an often-uncomfortable marriage of mostly civilian agencies tasked with defending the country's borders. Immigration and Customs Enforcement, the Coast Guard, the Transportation Security Administration and the Federal Emergency Management Administration all call DHS home.

"It has always been an internal conflict because you've brought together these major operating systems that had other responsibilities beyond counterterrorism, and so there's always been that balancing act," said Christian Beckner, the deputy director of the Homeland Security Policy Institute at George Washington University. “There's a natural tension there.”

Both Committee Chairman Sen. Tom Carper, D-Del., and ranking member Sen. Tom Coburn, R-Okla., have maligned the holes within the department. Carper called it “executive branch Swiss cheese.” Its inspector general position has been vacant for two years. Obama's recent appointment of Alejandro Mayorkas, the current head of immigration, to the No. 2 post would still leave a critical opening. And Mayorkas' nomination has been mired by an ethics investigation into his involvement with a controversial visa program.

Earlier this month, White House press secretary Jay Carney refused to speculate when the president would name a replacement for Napolitano, though recent reports suggest difficulty finding someone to take the job. Lawmakers on both sides of the aisle warn that the lack of long-term leadership is making matters worse.

The Government Accountability Office released a report last year noting morale was considerably lower among DHS employees than their counterparts at other agencies. Airport screeners and immigration agents tasked with identifying the nationality and eligibility of immigration applicants were particularly dissatisfied by their jobs.

Oversight of the department is fragmented, with about 100 committees and subcommittees claiming jurisdiction, DHS officials say. That has left agency heads scrambling to testify and fulfill dozens of committee requests while leaving it unclear where accountability ultimately lies.

The department's $60 billion budget, which has tripled since DHS was created, also has faced heavy scrutiny. Tom Ridge, the first DHS secretary under President George W. Bush, recently told the Senate committee he shared concerns about the growing budget and cautioned “more is not necessarily better.”

But the department also faces an evolving threat, and the bureaucracy built in response to the deadliest attack on U.S. soil is now shifting to fight cyber terrorism in the 21st century. The change in focus coupled with depreciating value of security equipment bought after Sept. 11 means resources are being spread thinner.

“That's going to be something that's a real challenge for the next secretary: meet the expectations of the stakeholders in terms of operations at airport, at borders, when you've already been stretching their budgets,” Beckner said.