Before Wednesday’s hearing on the attack in Benghazi, Libya, Republicans in Congress promised explosive new details about the administration’s mishandling of the episode. Instead, the hearing showed, yet again, that sober fact-finding is not their mission. Common sense and good judgment have long given way to conspiracy-mongering and a relentless effort to discredit President Obama and former Secretary of State Hillary Rodham Clinton.

The attack on the lightly protected consulate in Benghazi in September that killed Ambassador J. Christopher Stevens and three other Americans was a tragic event, and Americans should know the full story. The most authoritative account, completed in December, came from an independent inquiry, led by two respected and now retired officials — Thomas Pickering, a former deputy secretary of state, and Adm. Mike Mullen, a former chairman of the Joint Chiefs of Staff.

Their report was unsparing in concluding that “systemic failures and leadership and management deficiencies at senior levels” in the State Department’s bureaus of diplomatic security and near eastern affairs resulted in a “security posture that was inadequate for Benghazi and grossly inadequate to deal with the attack that took place.” Mrs. Clinton took responsibility for the security failures when she testified at a Congressional hearing in January.

Wednesday’s hearing, led by Representative Darrell Issa, a Republican of California who is chairman of the House oversight committee, featured three witnesses who testified about those failures. One of them, Gregory Hicks, the No. 2 official at the American Embassy in Tripoli, was at the embassy the night of the Benghazi attack. He said he was later demoted for raising questions about how the incident was handled, a charge the State Department denied.