Veterans Affairs Secretary Eric Shinseki faced tough questions from a Senate panel on Thursday about the state of his department after allegations that VA health clinics throughout the nation have cooked their books to cover up treatment delays.

The American Legion, the nation’s largest veterans-service group, has called on Shinseki and two other top VA officials to resign over the record-keeping controversy.

Below are some answers to a few key questions readers might have about this matter:

Why is Shinseki on the hot seat?

The Senate Veterans Affairs Committee called him to testify after multiple reports of preventable deaths and attempts to cover up treatment delays at VA health clinics. At least two whistleblowers have said a Phoenix VA hospital developed an elaborate scheme to keep delays out of its electronic database, possibly affecting dozens of patients who died while waiting for care.

Similarly, a report from the VA’s Office of the Medical Inspector said a department clinic in Fort Collins, Colo., falsified appointment records to give the impression that staff doctors saw patients within the agency’s goal of 14 days.

Veterans groups have also expressed concerns about a deadly Legionnaires’ disease outbreak at a Pittsburgh VA hospital in 2012 and reports that several patients died at an Atlanta clinic because of mismanagement. The VA inspector general’s report said the medical center was not sufficiently addressing patient safety.

Aside from the recent allegations, Shinseki is also tackling a backlog of longstanding disability claims — those that have remained in the system for more than 125 days without a determination. The VA has set a goal of eliminating that inventory by 2015, and the department reported this year that it had reduced it by 44 percent.

What has the VA done about the alleged cover-ups?

The department’s inspector general has launched an investigation of the allegations, and Shinseki ordered face-to-face audits of scheduling practices at all VA health clinics. The secretary has promised to take action on the reviews as soon as they are complete.

In the meantime, Shinseki has placed three of the Phoenix hospital’s executives on administrative leave “until further notice.”

How widespread is this problem?

The recent attention has focused on the allegations of wrongdoing in Phoenix and Fort Collins, but Senate Veterans Affairs Committee Chairman Bernie Sanders (I-Vt.) said Thursday that similar scandals have surfaced in at least 10 states.

The American Legion has documented those cases and others in a handy infographic that explains the evidence of wrongdoing and where the alleged problems occurred.

How long has the VA struggled with wait times?

Sen. Patty Murray noted during Thursday’s hearing that multiple Government Accountability Office reports dating back to 2000 have highlighted VA treatment delays. She said the department’s inspector general also looked at the issue in 2005, 2007 and 2012, determining each time that schedulers were not following VA policy.

The 2012 report said the department had not developed a reliable or accurate way of knowing whether its clinics were providing timely access to mental health care.

Where does the White House stand?

The White House has said President Obama remains confident in Shinseki’s ability to lead the VA and to take appropriate actions once the investigations are complete.

Obama on Wednesday directed his deputy chief of staff, Rob Nabors, to evaluate the VA’s scheduling practices, signaling the White House’s growing concern over the alleged cover-ups.

Nabors is perhaps best known for his work on the failed fiscal cliff deal. As the White House’s chief congressional liaison, he developed a reputation as a methodical wonk and quiet dealmaker who loves lists and despises leaks, according to a 2012 Washington Post profile.

Who is Shinseki?

Shinseki is a former four-star Army general and Vietnam War veteran who received two Purple Hearts for injuries he sustained during that conflict. He has headed the VA since January 2009.

As Army chief of staff, Shinseki famously clashed with top Pentagon officials over how many troops would be needed to occupy Iraq. He told the Senate Armed Services Committee in 2003 that the effort would require ” several hundred thousand soldiers,” but former Defense Secretary Donald Rumsfeld said the estimate would “prove to be high.”

Shinseki retired from the Army shortly after the fall of Baghdad in 2003, having served 38 years in the military.

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