Democrats have yet to say if they'll participate in what will be the eighth investigation since the attack on the U.S. diplomatic outpost in the eastern Libyan city.
Republicans say they need to find out why security was insufficient, what the president did the night of the attack, why the U.S. military didn't intervene, why initial explanations focused on a protest over a YouTube video and whether the administration deliberately sought to hide evidence about its conduct.
Some of the more contentious arguments made by the GOP members:
CHAIRMAN TREY GOWDY:
The second-term tea partyer and former prosecutor from South Carolina said two weeks ago there is evidence of a "cover-up." He cited a recently released email by White House national security communications aide Ben Rhodes.
He said the email "probably was the straw that broke the camel's back because that memo made it really clear we're going to blame an Internet video and not a broader policy failure in Libya." The White House has said Rhodes was referring to attacks across the Muslim world, not Benghazi specifically.
Gowdy has said former CIA Director Michael Morell "sanitized" a series of talking points used by then-U.N. Ambassador Susan Rice five days after the violence, substituting the term "extremist" for all references to "terrorist," and "demonstration" for "attack." Republicans say this was part of an effort by President Barack Obama's team to play down a major terrorist attack in the final weeks of his re-election campaign.
In April, Morell testified that he made no changes to provide political benefit to Obama or then-Secretary of State Hillary Rodham Clinton, who is considering running for president in 2016. He said the CIA considers extremist and terrorist as synonyms, and that references to al-Qaida in the talking points were avoided to protect classified sources.
REP. MARTHA ROBY:
The 37-year-old Alabama congresswoman, attorney and daughter of a federal judge led the House Armed Services Committee's investigation. That panel rejected claims by conservatives that the military failed to respond the night of the attack — putting her at odds with other Republicans.
Her investigative panel concluded in a report in February that there was no "stand down" order issued to military personnel in Tripoli, the Libyan capital, who wanted to aid Americans in Benghazi. Select committee colleagues Gowdy and Rep. Jim Jordan have suggested otherwise.
"We simply were not postured to respond in time," Roby said seven months ago.
REP. LYNN WESTMORELAND:
The Georgia congressman also is a veteran of a Benghazi investigation, one conducted by the House Intelligence Committee. In April 2013, he issued a news release describing his "two conclusions": that Clinton personally denied much-needed additional security for U.S. diplomats in Libya and that White House officials perpetuated a "lie" about the anti-Muslim film "to protect their own backsides."
Westmoreland pointed to a department cable declining security requests "signed" by Clinton. The conclusion has been widely challenged. The secretary of state's name is routinely attached to State Department correspondence from Washington, most of which he or she never sees or is consulted on. Lower-level department officials have said they were responsible for specific security decisions related to Benghazi.