New evidence of mismanagement and delays in veterans' healthcare has piled up, nearly a year since President Obama vowed to clean up arguably the most beleaguered department in his administration.

For the White House, the ouster of Veterans Affairs Secretary Eric Shinseki last May was supposed to represent the beginning of an overhaul to an agency that became a symbol of bureaucracy run amok.

Instead, auditors have found marginal improvements, calling for a fresh round of investigations into why backlogs in disability claims appear so systematic — and why a cover-up culture persists.

A group of nine senators released a scathing report recently, calling for an investigation into each of the VA's 56 regional offices. The lawmakers highlighted findings that VA workers in Philadelphia manipulated data, calling them proof that shortcomings had hardly been snuffed out.

"The VA needs to cut red tape, make the paperwork easier and rid itself of the culture that's led to the current backlog of disability claims," Sen. Pat Toomey, R-Pa., said, of healthcare for veterans in his home state. "It's outrageous to leave our veterans in limbo for more than four months on average waiting for initial feedback."

Lawmakers are growing increasingly frustrated with the Obama administration's handling of the problems.

When Obama tapped Robert McDonald to replace Shinseki, Republicans applauded the choice and expressed optimism that lasting improvements would soon follow.

Those at the center of the debate, however, say the administration has done little to punish those responsible for the department's abysmal performance.

Documents provided to the House Veterans Affairs Committee last month showed that just three people had been fired for doctoring data to make it look as though treatment was delivered on time.

The Washington Examiner first reported that more than 1.5 million medical records were destroyed at veterans hospitals without proof that patients received any medical care.

The Phoenix VA hospital, which Obama visited in March, became ground zero in one of the most damaging scandals to his administration.

"We all know that there have been significant problems at this facility," Obama said during the trip. "The kind of cooking the books and unwillingness to face up to the fact that veterans were not being adequately served went on too long."

Perhaps the most worrying sign to lawmakers is that problems similar to those unveiled in Phoenix have mushroomed to other areas of the country.

The VA's inspector general found in April that at least half of the department's 10 worst-performing regional offices had falsified information about patients' waiting times or committed similar offenses.

And lawmakers are accusing VA leadership of resisting requests for information about what went wrong in Philadelphia, for example.

"It is the VA's actions to stonewall this committee — actions that began long before your tenure as secretary, and continue to occur today — which has eroded the confidence of veterans and the American people in our ability to work together," Rep. Jeff Miller, R-Fla., chairman of the committee, wrote McDonald.

"I trust that through VA's immediate cessation of its groundless efforts to withhold information, we can rebuild that confidence."

Critics argue that Obama's commitment to fixing the VA problems has been lacking, accusing him of exaggerating improvements at the agency.

"The supposed progress being reported by the VA on the benefits backlogs is a classic shell game. Rather than properly processing dated benefit claims, the [administration's] own numbers show it is simply throwing backlogged claims in to the appeals process to give the appearance of progress," said Dan Caldwell, legislative and political director at Concerned Veterans for America. "As the backlog numbers decrease, the number of appeals being filed by veterans awaiting benefits has steadily increased to the point that they will soon double the number of claims over four months old."