At the international military headquarters in Kabul, it's jokingly being called the curse of the commander's job.
The last four U.S. generals to run the Afghan war were either forced to resign or saw their careers tainted by allegations of wrongdoing.
The first, Gen. David McKiernan, was ousted on May 11, 2009, a year before his term as commander was set to end. Then-Defense Secretary Robert Gates wanted McKiernan's resignation as newly elected President Barack Obama launched a counterinsurgency strategy of working to undermine the Taliban's pull on the population.
It was the first presidential dismissal of a wartime general since President Harry Truman ousted Gen. Douglas MacArthur during the Korean War.
Obama replaced McKiernan with Gen. Stanley A. McChrystal, who had a background in special operations and came in with a mandate to remake the war effort with the help of "surge" troops. But he lasted only 13 months.
In June 2010, Rolling Stone published an article that quoted scathing remarks McChrystal and his aides made about their civilian bosses, including Vice President Joseph Biden, as fools who were ignorant of the complexities of war. Obama called McChrystal back to Washington to explain and forced him to resign.
Gen. David Petraeus took over the Afghan command in July 2010 to fill the void left by McChrystal's abrupt departure and agreed to serve for one year. He completed that term and then retired from the military to become CIA director in September 2011.
Petraeus resigned as CIA director on Nov. 9 after he had an extramarital affair with his biographer. The affair came out as part of an FBI investigation into suspicious emails between the biographer and another woman.
The current chief, Gen. John Allen, was appointed by Obama to oversee the drawdown of U.S. and international forces ahead of the planned transfer of security responsibility to the Afghan government in 2014.
Pentagon officials said Tuesday that Allen, 58, is under investigation for thousands of alleged "inappropriate communications" with the second woman involved in the Petraeus case, a Florida socialite. Allen's nomination to become the next commander of U.S. European Command and the commander of NATO forces in Europe has now been put on hold.
Expecting Allen to be confirmed for his new post, Obama had already chosen Gen. Joseph Dunford succeed him. If confirmed, Dunford would be the 15th top commander there since 2002, a revolving door of generals that some analysts say is detrimental to the war effort.
"Rotating top commanders on an annual basis makes no management sense," Thomas E. Ricks, a senior fellow at the Center for a New American Security, wrote in an opinion piece published Sunday in The New York Times. "Imagine trying to run a corporation by swapping the senior executives every year. Or imagine if, at the beginning of 1944, six months before D-Day, Gen. George C. Marshall, the Army chief of staff, told Gen. Dwight D. Eisenhower, the supreme allied commander, that it was time to give someone else a chance to lead."
When Petraeus took the helm as coalition commander on July 4, 2010, he proclaimed: "We are in this to win."
Petraeus relied heavily on air strikes and night raids. But the emphasis on killing and capturing militants worked better than the other main part of the strategy, which was to clear the Taliban out of a particular territory, then focus on holding and developing it to win over the local Afghan population.
Since he took charge, Allen has been confronted with a series of U.S. tragedies and missteps that have hindered the U.S. campaign in Afghanistan, where militants, while weakened, continue to conduct their trademark suicide attacks and roadside bombings.
A month after he assumed his command, insurgents shot down a Chinook helicopter in eastern Afghanistan, killing 30 American troops and seven Afghan commandos and a translator. It was the single deadliest loss in the war.
In January, a video purportedly showing American Marines laughing and urinating on the corpses of Taliban fighters surfaced on the Web.
In February, Muslim holy books were burned at a U.S. base north of Kabul. Obama called the incident a terrible mistake, but it triggered scores of anti-American protests across the country, leaving more than 30 Afghans and six U.S. soldiers dead.
In March, a U.S. soldier allegedly went on a shooting rampage in two villages in southern Kandahar province, killing 16 villagers.
In June, Allen traveled to eastern Logar province to personally deliver his regrets about a NATO airstrike that Afghan officials said killed 18 civilians.
The events have shattered the Afghan people's trust in America and have driven a dagger into the U.S.-led coalition's hearts-and-minds campaign, which was already in decline after years of war. Coalition forces will still help bolster the Afghan government and security forces in the coming years, but Afghans increasingly believe America's only mission is to leave as soon as it can.
Allen also had to contend with a spike in insider attacks by Afghan forces, or insurgents in their uniforms, on their foreign allies and even on their Afghan colleagues. The attacks have raised questions about how effectively the allied forces can train the Afghans to take over security of their own country in 2014.
The news about the Allen investigation broke in Kabul just a few hours after militants fired four rockets on the Afghan capital, killing one Afghan man and wounding three other people.
Waheed Muzhda, a former foreign ministry official under the Taliban regime, said Petraeus' affair is evidence that American civilization is crumbling.
"It is shameful for a military general with such a big name and authority to violate the rights of his wife," Muzhda said. "These types of values are totally different from the values of Islam and our culture. ... If this happens in our country, the punishment is stoning."
Mullah Maulvi Habibullah, a well-known Muslim cleric in Kabul, said the affair tarnishes the dignity of the CIA around the world.
"Such immoral sexual relations take place in societies with no Islamic values," he said. "The U.S. has no such authority or dignity to (say they want to) bring human rights and women's rights to the world."
In neighboring Pakistan, Akhlaq Ahmad, who works at an electric company in the southern city of Karachi, said Pakistani officials could learn a lesson from Petraeus' decision to resign.
"In this matter, America proved to be on high moral ground and also proved that law and moral ethics apply to every citizen equally," Ahmad said. "If we compare it with Pakistan we should be shameful and learn a lesson from this."
Associated Press writers Patrick Quinn, Slobodan Lekic, Amir Shah and Rahim Faiez in Kabul, Robert Burns in Perth, Australia, Adil Jawad in Karachi, Pakistan, and Riaz Khan in Peshawar, Pakistan contributed to this report.