The U.S. House Select Committee on Benghazi, after grilling former Secretary of State Hillary Clinton for 11 hours on Thursday to little effect, must take a step back now and decide what is next in the investigation of an incident that is now three full years in the nation's past.

To date, a total of five House committees, two Senate committees and a State Department independent review board have examined the internal problems leading to the attack on the U.S. mission at Benghazi that took the lives of four Americans, including U.S. Ambassador Chris Stevens.

The House Select Committee itself has spent 18 months, 21 hearings and nearly $5 million attempting to fix blame. In that time, too little has been done to examine the systemic issues that led to an unofficial, under-secured diplomatic mission being left to face growing unrest in a region of the world known for violent action.

Too much time has been spent on rhetorical grandstanding and blatant attempts to undermine the credibility of the Democratic front- runner for president. Clinton acquitted herself well under pressure Thursday and, in a consequence unintended by the GOP, has galvanized many Democrats who had been soft in their support.

But the committee's time has not been entirely wasted. It did a service by unearthing the fact that as secretary of state, Clinton used a private e-mail server, bypassing the official State Department communications system, although there is no evidence Clinton transmitted classified information via those e-mails.

There's also this nugget: On the night of the attack, when the State Department's official line was that the uprising had been sparked by a video, Clinton sent a private e-mail to her daughter Chelsea that stated, seemingly without equivocation, that "two of our officers were killed in Benghazi by an Al-Qaida-like group." Clinton on Thursday attributed the inconsistencies to "the fog of war," and at one point said, "I believe to this day the video played a role."

But what now? None of the investigations has yet found any evidence that the State Department willfully jeopardized the safety of the mission. It's true that Stevens had requested additional security, which he did not get. It is also true that Congress had previously cut funding requests for diplomatic security. There is, it appears, enough blame to go around.

That is a lesson this Congress appears to have forgotten. Attacks on American embassies and outposts are not new. In 1983 the American embassy in Beirut was bombed, with 63 dead — including 17 Americans. The embassy was moved and attacked a second time. Then came the suicide bombing of Marine barracks in Beirut later that year. In response, the House launched a two-month investigation that found serious judgment errors in the Marine chain of command. The embassy bombing prompted a report that focused on improving security measures.

There have been many attacks since then. Yemen. Pakistan. Serbia. Nairobi. Kenya. None has prompted the granular dissection we're seeing now. What we do know is that two Republicans and one former staffer have acknowledged that the committee was formed in part to drive down Clinton's chances as a viable presidential contender.

To restore its own credibility, the committee must now focus, in a nonpartisan way, on what lessons can be learned from Benghazi that might better protect the nation's diplomatic efforts abroad. Failing that, it should call a halt to what looks like a fruitless attempt to sabotage a campaign while using U.S. government resources.