Secretary of Veterans Affairs Robert McDonald, seen here last November, has acknowledged that he was wrong when he said he had been in the special forces. Chuck Myers/Landov hide caption

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A U.S. Air Force C-123 sprays herbicides on dense jungle beside a South Vietnamese highway on May 18, 1966. This aircraft is the last in a formation of three. Spray from the other two planes can be seen ahead. U.S. Air Force via AP hide caption

itoggle caption U.S. Air Force via AP

Secretary of Veterans Affairs Robert A. McDonald attends a news conference after a visit to the James A. Haley Medical Center in Tampa, Fla., last month. Chris O'Meara/Associated Press hide caption

itoggle caption Chris O'Meara/Associated Press

Soldiers returning from the Pacific wave from the deck of the USS General Mitchell on Dec. 11, 1945. Much of the health care demand in the VA system is from veterans of earlier wars. AP hide caption

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Sen. John McCain discussed the Veterans Choice Act at a news conference on Tuesday, with fellow Arizona Republican Sen. Jeff Flake. Mark Wilson/Getty Images hide caption

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Secretary of Veterans Affairs Eric Shinseki addresses the National Coalition for Homeless Veterans in Washington, D.C., Friday, shortly before he resigned under bipartisan pressure. Win McNamee/Getty Images hide caption

itoggle caption Win McNamee/Getty Images