To congressional Republicans, “Benghazi” is shorthand for incompetence and cover-up. Democrats hear it is as the hollow sound of pointless investigations.

It is, in fact, a Mediterranean port city in Libya that was the site of a deadly attack on an American diplomatic compound on the 11th anniversary of 9/11 that killed U.S. Ambassador Chris Stevens and three other Americans. That’s nearly all that U.S. politicians can agree on about Benghazi.

It’s been a political rallying cry since just weeks before President Barack Obama’s re-election in November 2012. With the launch of a new House investigation, Benghazi is shaping up as a byword of this fall’s midterm election and the presidential race in 2016, especially if former Secretary of State Hillary Rodham Clinton is on the ballot.

A guide to the controversy:

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SETTING THE SCENE

The 2011 revolt that deposed and killed Libyan dictator Moammar Gadhafi, with the help of NATO warships and planes, began in Benghazi. A year later, the city of 1 million remained chaotic, in the grip of heavily armed militias and Islamist militants, some with links to al-Qaida.

The temporary U.S. diplomatic mission, created in hopes of building ties and encouraging stability and democracy, was struck by homemade bombs twice in the spring of 2012. British diplomats, the Red Cross and other Westerners were targeted that spring and summer.

Stevens, based in the capital city of Tripoli, chose to visit Benghazi on the anniversary of the Sept. 11, 2001, attacks, when U.S. embassies around the world were on alert for terrorism.

In Egypt that day, a different sort of trouble struck, and would spread to other Mideast cities over several days: Protesters angry about an anti-Muslim video made in America stormed the U.S. Embassy in Cairo, clambering over the walls and setting flags on fire.

Hours later, the assault in Benghazi began.

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A FIERY ASSAULT AND FOUR DEATHS

The Benghazi attack came in three waves, spread over eight hours at two locations. Only in hindsight is the duration of the attack clear because of a lengthy pause before the second assault.

According to accounts from congressional investigators and the State Department’s Accountability Review Board:

Around 9:40 p.m. on Sept. 11, a few attackers scaled the wall of the diplomatic post and opened the front gate, allowing dozens of armed men in. Local Libyan security guards fled. A U.S. security officer shepherded Stevens and Sean Smith, a State Department communications specialist, into a fortified “safe room” in the main building.

Attackers set the building and its furniture afire with diesel fuel. Stevens and Smith were overcome by blinding, choking smoke that prevented security officers from reaching them. Libyan civilians found Stevens in the wreckage hours later and took him to a hospital, where he, like Smith, died of smoke inhalation.

He was the first U.S. ambassador to be killed in the line of duty in more than 30 years.

A security team from the CIA annex about a mile away arrived to help about 25 minutes into the attack, armed only with rifles and handguns. The U.S. personnel fled with Smith’s body back to the annex in armored vehicles.

Hours after the first attack ended, the annex was twice targeted by early-morning mortar fire. The second round killed Tyrone Woods and Glen Doherty, two CIA security contractors who were defending the annex from the rooftop.

A team of six security officials summoned from Tripoli and a Libyan military unit helped evacuate the remaining U.S. personnel on the site to the airport and out of Benghazi.

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THE FALLOUT BACK HOME

Word hit Washington in the final weeks of the presidential race. Over the next several days, the Benghazi news blended with images of angry anti-American demonstrations and flag-burnings spreading across the Middle East over the offensive video.

Political reaction to the Benghazi attack quickly formed along partisan lines that hold fast to this day.

Republican presidential nominee Mitt Romney and others said Obama had emboldened Islamic extremists by being weak against terrorism. But the public still credited Obama with the successful strike against al-Qaida leader Osama bin Laden a few months earlier in Pakistan.

The accusation that took hold was a Republican charge that the White House intentionally misled voters by portraying the Benghazi assault as one of the many protests over the video, instead of a calculated terrorist attack under his watch.

Obama accused the Republicans of politicizing a national tragedy. He insists that the narrative about the video protests was the best information available at the time.

After 13 public hearings, the release of 25,000 pages of documents and 50 separate briefings over the past year and a half, the arguments are the same.

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WHO WAS TO BLAME FOR LEAVING THE DIPLOMATIC POST SO VULNERABLE?

Republican and Democratic lawmakers agreed: The State Department under Clinton kept open the Benghazi mission, which employed a few State Department workers and more than two dozen CIA workers, with little protection in the midst of well-known dangers.

The attack probably could have been prevented if the department had heeded intelligence warnings about the deteriorating situation in eastern Libya, a bipartisan report by the Senate Intelligence Committee said.

Stevens’ requests for more security, made clear in cables to State Department headquarters in July and August 2012, went unheeded, according to the Senate report, as did those made by his predecessor earlier that year.

But Stevens also twice declined the U.S. military’s offer of a special operations team to bolster security and otherwise help his staff.

The month after the attack, Clinton said she was responsible for the safety of those who had served in Benghazi, without acknowledging any specific mistakes on her part. Obama said the blame ultimately rested on his shoulders as president.

Yet the administration says neither Obama nor Clinton was aware of the requests for better protection in Benghazi because they were handled at lower levels.

Four senior State Department officials were put on paid leave after an independent board investigating the attack said security at the Benghazi mission was “grossly inadequate.” After a review, the department says it reassigned three officials to positions of lesser responsibility; one resigned.

Some Republicans complained that no one was fired.

Democrats tried to shift some blame to GOP lawmakers, complaining that they had cut the administration’s budget request for diplomatic security in 2012.

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WHY DIDN’T THE MILITARY COME TO THE RESCUE?

No military resources were in position to counter the surprise attack, the bipartisan Senate review found.

The military sent surveillance drones that relayed information to the security officers on the ground. It began moving Marines and special forces toward Libya, but the surviving American personnel were evacuated before they could arrive. Two Defense Department personnel arrived from Tripoli to help transport the Americans to the Benghazi airport.

The Senate panel rejected claims that the military had been ordered to “stand down” as the tragedy unfolded.

That persistent allegation has divided Republican lawmakers.

Some continue to pursue the theory that an order from on high blocked possible military action, such as rushing more personnel from Tripoli or scrambling fighter jets from Italy. Other Republicans, including members of the House Armed Services Committee, have accepted assurances from the Pentagon that nothing more could be done in time.

The bipartisan committee did fault the military, however, for failing to anticipate the possibility of such an emergency in Benghazi and not being ready.

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DID OBAMA INTENTIONALLY MISLEAD AMERICANS?

Obama’s opponents are focused on the “talking points,” a memo prepared for lawmakers and for then-U.N. Ambassador Susan Rice to help her get ready for appearances on the Sunday news shows to discuss the attack less than a week after it occurred.

That memo is offered as evidence of a possible White House cover-up. It offers something that’s golden to investigators — a paper trail.

Last year, the administration reluctantly released 100 pages of emails documenting the administration’s editing of the talking points, first composed by the CIA. The final version omitted references to possible al-Qaida influences in the attack and retained the theory that it grew out of a street protest.

On television, Rice described the attack as a “horrific incident where some mob was hijacked, ultimately, by a handful of extremists.” Since then, numerous investigations have concluded there were no protesters outside the Benghazi compound before the armed assault.

Republicans argue that the administration already knew that. The White House says Rice was giving the best information available from intelligence agencies at that time.

Two months after her TV appearances, the controversy ended Rice’s chance to follow Clinton as secretary of state. Obama instead named her his national security adviser.

In April, another email showing the White House’s efforts at political damage control surfaced among documents released under a Freedom of Information Act lawsuit. Republicans charge that the administration had withheld the email in violation of an earlier congressional subpoena. White House press secretary Jay Carney contended that the email, part of the talking points collection, focused on the overall Mideast protests, not Benghazi.

The email says one of Rice’s goals is “to underscore that these protests are rooted in an Internet video, and not a broader failure of policy” and includes the assertion that the Benghazi assault apparently grew out of a street demonstration.

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“WHAT DIFFERENCE, AT THIS POINT, DOES IT MAKE?”

As the presumed front-runner for the Democratic presidential nomination in 2016, Clinton is the prime political target of the Benghazi probes.

Rep. Trey Gowdy, R-S.C., chosen to lead a new House select committee on Benghazi, acknowledges that its work may continue into the presidential campaign season. House Democrats are deeply divided over whether to participate in the probe, which their leader, Rep. Nancy Pelosi of California, calls a “political stunt.”

If it achieves nothing else, the Benghazi investigation will cloud Clinton’s record and force her to watch every word. Critics already have latched onto her what-difference-does-it-make moment at a Senate hearing.

Here’s what she said, under questioning from Sen. Ron Johnson, R-Wis., about why the State Department didn’t quickly call the evacuees and ask whether there had been protesters outside the compound before repeating that story on the Sunday talk shows:

“With all due respect, the fact is we had four dead Americans,” Clinton said with evident exasperation. “Was it because of a protest or was it because of guys out for a walk one night who decided that they’d they go kill some Americans? What difference, at this point, does it make? It is our job to figure out what happened and prevent it from ever happening again, senator.”

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AN UNFINISHED STORY

No one has been arrested for the Benghazi attack.

The administration has named two militant groups that officials believe were among the attackers. One is led by a former Guantanamo Bay detainee, Sufian bin Qumu, who was released from the U.S. military prison in Cuba in 2007. He was described by officials there as “a probable member of al-Qaida.”

The suspected groups are considered ideological cousins of the terrorists behind the 2001 attacks on New York and Washington. But State Department officials say they don’t think core al-Qaida leaders orchestrated the Benghazi attack.

The administration says it won’t give up on bringing the assailants to justice.

Since the Benghazi mission was burned, the rebel brigades that once fought Gadhafi’s forces have hardened into increasingly powerful militias, many made up of Islamic extremists. Libya’s central government is weak, security forces can’t maintain control, and bombings and shootings continue.

The State Department maintains the U.S Embassy in Tripoli but hasn’t returned to Benghazi.

(AP)