Originally printed in The Wall Street Journal, May 15th, 2013 

In January, for the first time since the Benghazi terrorist attack of Sept. 11, 2012, Hillary Clinton faced the Senate Foreign Relations Committee to testify about the attack. In response to my persistent questioning about what the State Department knew about the nature of the attack, the former secretary of state famously exclaimed: "What difference, at this point, does it make?"

New testimony by State Department whistleblowers and an Interim Progress Report prepared by five House Committees show what a huge difference it makes when members of the administration ignore repeated warnings of growing danger, deny requests for additional security and then attempt to cover up their negligence. That dereliction of duty ultimately resulted in the death of four Americans.

While the whistleblowers' testimony is gripping, the House report also is well worth reading. Collectively, the five committees reviewed tens of thousands of classified and unclassified documents, cables, emails and reports. They interviewed dozens of individuals with firsthand knowledge of the events. Their findings, although far from complete, are damning.

In public, Mrs. Clinton has claimed "full responsibility" for the attack in Benghazi. But in testimony before Congress, she shielded herself with a report by the Accountability Review Board and pinned the blame on unnamed State Department officials a few levels below her. "I have made it very clear that the security cables did not come to my attention or above the assistant secretary level where the ARB placed responsibility," Mrs. Clinton said on Jan. 23, 2013.

Yet, an April 19, 2012, State Department cable responding to former Ambassador Gene Cretz's request for additional security in Benghazi bears Mrs. Clinton's signature. That cable specifically acknowledges Mr. Cretz's request for additional security, and "stipulates that the plan to drawdown security assets will proceed."

There was a steady stream of warnings about the deteriorating security situation in Benghazi from the U.S. intelligence community. The British, the United Nations and the International Committee of the Red Cross had removed their personnel. Libya was an obvious hot spot, and 9/11 was a day to be on high alert. And yet we are supposed to believe that none of this required or received the attention of the secretary of state? If it is true Mrs. Clinton was so profoundly uninformed, then it would also be true she was profoundly negligent.

When she wasn't hunkered down in the days following the attack, maintaining strategic silence due to an "FBI investigation," she stuck to the administration talking point that the attack was a spontaneous protest. She repeatedly referred to the YouTube video—even telling the father of slain American security officer Tyrone Woods that the producer of the video would be brought to justice.

President Obama's re-election narrative was that Osama bin Laden was dead, al Qaeda was decimated, and Libya proved the success of his "leading from behind" strategy. Despite the warnings, the administration ramped down security in Benghazi. It's no wonder Mrs. Clinton would want to keep her head down following the attack and make every attempt to misdirect attention from the administration's negligence.

The natural reaction of any leader when a subordinate loses his life in the line of duty is to talk to anyone who could explain what happened. That's why, in January, I asked Mrs. Clinton why she didn't just call the survivors to find out the facts.

At first, I assumed her exasperated response revealed that she knew she should have made those calls. But with the revelations of the Interim Progress Report and testimony, it is becoming clear her reaction—and the behavior of President Obama and his administration—was designed to mask their failure of leadership. Instead of making a call to acting Ambassador Gregory Hicks, Mrs. Clinton and the White House sidelined him, leaving him "stunned" and "embarrassed" as he watched Susan Rice's Sunday show appearances, as he put it to Congress last week.

Thanks to the bravery of Mr. Hicks and his colleagues, the truth about Benghazi is beginning to be revealed. But more survivors need to be able to tell their stories. Some are contract employees who will need whistleblower protection, and some are current or former administration officials whose testimony may need to be compelled by subpoena.

A congressional Joint Select Committee can offer that protection and issue those subpoenas. Such a committee should be appointed without further delay, so that the full story of Benghazi can be told and so such a fiasco never happens again.

Mr. Johnson is a Republican senator from Wisconsin.

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