Veterans Affairs Secretary Eric Shinseki testified before the Senate Thursday on VA health clinics allegedly covering up treatment delays. (The Washington Post)

Veterans Affairs Secretary Eric K. Shinseki stared, at times impassively, at a panel of senators who repeatedly hammered him Thursday over long waits for veterans seeking care and reports of coverups at VA medical centers.

When it was his turn to speak, Shinseki vowed to remain in office as long as he has President Obama’s support. He told the lawmakers that the allegations of impropriety made him “mad as hell.”

“I could use stronger language, Mr. Chairman, but in deference to the committee, I won’t,” Shinseki told the Senate Veterans’ Affairs Committee.

The VA medical system, which conducts more than 230,000 appointments every day, is the country’s largest and has been dogged for years by complaints from veterans about months-long waits for appointments. Shinseki, a former Army general who was wounded in Vietnam, was brought in by Obama to change VA’s culture and make it more responsive to veterans’ needs.

“I came here to make things better for veterans,” Shinseki told the senators Thursday. “This is not a job. I’m here to accomplish a mission.”

Shinseki, however, has faced enormous challenges that have often overwhelmed the sprawling VA bureaucracy. In addition to contending with a growing number of older veterans, the department has had to provide care and services for a new generation of Iraq and Afghan war veterans who are filing disability claims and seeking treatment for mental and physical wounds at rates significantly higher than those who fought in previous wars.

Now, Shinseki is being buffeted by many of the same problems that have bedeviled his predecessors.

The most recent series of scandals, which have stoked calls for Shinseki to resign, began with allegations that VA health clinics in Phoenix and Fort Collins, Colo., used elaborate schemes to hide the records of patients who waited months for care.

Before Shinseki began his testimony Thursday, Republicans and Democrats took turns expressing their deep dismay with the department and, in some cases, Shinseki’s leadership.

“It seems that every day there are new allegations,” said Sen. Richard Burr (N.C.), the top Republican on the panel.

Sen. Patty Murray (D-Wash.) spoke of “systemwide problems,” saying: “This needs to be a wake-up call for the department.”

The VA inspector general’s office is investigating the allegations made against health clinics in Phoenix, and Shinseki promised that he would act swiftly and aggressively if the charges proved true.

But Shinseki, who has a reputation for cautious and steady leadership, stopped short of making any promises to fire senior VA leaders or change his management team. “I don’t want to get ahead of myself or ahead of the IG here,” he said. “I want to see the results of the audit.”

While there were no demands for Shinseki’s departure at the hearing, Republican congressional candidates on the campaign trail began raising concerns about the secretary, possibly making it more difficult for lawmakers to continue supporting him.

Sen. Johnny Isakson (R-Ga.), a member of the Veterans’ Affairs panel, expressed tenuous support for Shinseki. “I like Eric an awful lot, but I can’t believe the lack of knowledge of some of the things that were obvious and apparent within the system,” he said. “He’s either been ill-served by his senior leadership — which I think is part of the systematic problem — or has been oblivious to what’s been going on around him.”

In recent weeks, reports have spread of VA hospital officials falsifying records or gaming the system to make waiting times appear shorter. The reports began appearing as long ago as 2010, when a senior VA official sent a memo to regional directors warning of “inappropriate scheduling practices” designed to make waiting times appear shorter.

In response to the growing scandal, Obama has dispatched one of his closest advisers to oversee a review of the department. Rob Nabors, a White House deputy chief of staff, will work with VA temporarily to help assess its practices and develop recommendations on how veterans’ hospitals can increase access to timely care, the White House said Wednesday.

The move, however, wasn’t nearly enough to quiet VA critics on both sides of the aisle in Congress or the veterans groups such as the American Legion and Concerned Veterans for America that have called for Shinseki’s resignation.

Sen. John McCain (R-Ariz.) complained that the department’s failure has produced a “crisis of confidence” in the veterans community. “No one should be treated this way in a country as great as ours.” he said.

“The standard practice at the VA seems to be to hide the truth in order to look good,” said Murray. “That has got to change once and for all.”

Shinseki, meanwhile, did not promise the kind of broad, sweeping and systemic changes that senators and some veterans groups had hoped for. Instead, while expressing concern about allegations of wrongdoing, he defended the quality of care that VA provides and noted that veterans’ overall satisfaction with their medical treatment is “equal to or better than the rankings for private-sector hospitals.”

Ed O’Keefe and William Branigin contributed to this report.