How much longer?
Most likely, the war will go on for years, say many commanders and military analysts. In fact, it's possible to consider this just the midpoint. The U.S. combat role in Iraq could have another half decade ahead - or maybe more, depending on the resilience of the insurgency and the U.S. political will to maintain the fight.
Iraq, experts say, is no longer a young war. Nor it is entering an endgame. It may still be in sturdy middle age.
"Four years, optimistically" before the Pentagon can begin a significant troop withdrawal from Iraq, predicted Eric Rosenbach, executive director of the Center for International Affairs at Harvard's Kennedy School, "and more like seven or eight years" until Iraqi forces can handle the bulk of their own security.
What that means depends largely on your vantage point.
For the Pentagon, it's about trying to build up a credible Iraqi security force while struggling to support its own troop levels in a military strained by nonstop warfare since 2001. During a trip through the Persian Gulf last year, Adm. William Fallon, then head of U.S. Central Command, was peppered with as many questions about resources as about strategies moving ahead.
For many Americans, it's about a rising toll - nearly 4,000 U.S. military deaths and more than 60,000 wounded - with no end in sight. Iraqis count their dead and injured in much higher figures - hundreds of thousands at least - and see entire neighborhoods changed by the millions who have fled for safer havens.
For others, it's about an ever-mounting loss of goodwill overseas: "We've squandered our good name," says 29-year-old Ryan Meehan, sitting in a St. Louis coffee shop.
You can also frame the war in terms of the cost to the treasury: $12 billion a month by some estimates, $500 billion all together, and the prospect of hundreds of billions more.
But then there's other measures of the war as it enters its sixth year.
These are more difficult to weigh - yet are just as real and profound - and are found in places such as Jim Durham's home in Evansville, Ind. He tries to fight off a sense of dread as he watches his 29-year-old son prepare for his second tour in Iraq with the Indiana National Guard.
Durham, 59, struggled to describe the emotions. He decided: "It's like watching somebody with a disease."
"Perhaps they can live, perhaps they can't," he said. "Maybe they'll survive. Maybe they won't. And there's nothing you can do about it."
Echoes of the same lament resounded at a Shiite funeral procession in Baghdad where mourners gathered their dead from the morgue - the bodies washed for burial according to Muslim custom - after bombings ravaged two pet markets last month. "We are helpless. Only God can help us," cried a group of women behind the shrouded corpses of several children.
"How much can Iraq endure? How much stamina do Americans have for a war with no end in sight?" said Ehsan Ahrari, a professor of international security at the Asia-Pacific Center for Security Studies in Honolulu. "These questions were relevant years ago. They only grow more critical as the years go by."
"War fatigue is real, first and foremost because of casualties," said Michael O'Hanlon, a foreign policy scholar at the Brookings Institution. "But Americans also know the stakes."
Some remain determined. Ahrari recalls seeing a couple at the Gulfport, Miss., airport saying goodbye to their son, clad in desert camouflage and heading for Iraq. He can't forget the mother's face: grim but stoic.
"She did not seem sure that her son was going to the right place to serve America," he wrote, "but that it was still a right thing to do."
But then there was the group of women on a bridge in New Smyrna Beach, Fla., holding "No to War" placards and being alternately cheered and jeered.
And Catherine Lunsford Hanley, 26, of Roanoke, Va., who is so worried about her husband in Iraq that she's suffering hair loss and insomnia. Thinking that the war will continue - and maybe force a second deployment for her husband - makes it even worse.
"It'll kill me if we have to go through this again," she said.
And Vietnam veteran Wilbur Taylor breaking down in tears at a VFW post in Evansville, Ind., as he thinks of the young soldiers in Iraq. "It's an endless battle," sobbed Taylor, 59.
He's not far wrong.
Already, the war has lasted longer than the U.S. fight in World War II and Korea. And if many experts are to be believed, the Iraq war will follow roughly a 10-year arc, ending only after a new crop of soldiers - some now barely into their teens - is on the battlefield.
The halfway scenario is based on historical templates. Many military strategists cite a nine- to 10-year average for insurgencies, with expected drop-offs in recruitment and core strength after a decade.
But the models - analyzing battles from the British in Malaysia in the 1950s to the Soviets in Afghanistan in the 1980s - also show that each fight is unique. Kurdish rebels have been fighting in Turkey more than 20 years, and the FARC guerrillas have been active in Colombia since the 1960s.
The fragmented nature of the Iraq fighting - what's been called a "mosaic war" - also may add years to U.S. involvement. The different tactics needed for various regions create difficulties in training Iraqi forces and making decisive strikes against insurgents such as al-Qaida in Iraq.
At West Point, professor Brian Fishman is an expert in al-Qaida. He tells his cadets that Iraq war is now fundamentally "a collection of local wars" to preserve key local alliances with Iraqi groups and keep pressure on insurgents from regaining footholds.
"Iraq is a fight that, no doubt, is evolving," said Fishman after teaching his class for the Combating Terrorism Center at the U.S. Military Academy. "But when you talk about some kind of end for American troops, it's certainly in terms of years."
The cadets in his class were in high school the first U.S. bombs fell on Iraq. They know they could be well into their military careers before it's over.
Lt. Gen. Raymond Odierno, the former No. 2 commander in Iraq, said in January that U.S. aircraft could be used to support Iraqi combat operations for "five to 10 years" along with "an appropriate number of ground forces."
That same month, Lt. Gen. James Dubik, who heads the Multi-National Security Transition Command, told the House Armed Services Committee that Iraqi officials estimate they can't assume responsibility for internal security until as late as 2012 and won't be able to defend Iraq's borders until 2018.
The insurgency, however, may not be the most worrisome problem in coming years. Some believe the worst struggle will be keeping friction between Iraq's Sunnis and Shiites from ballooning into civil war.
"I don't know anyone who pays serious attention to Iraq who thinks that we are over the hump in terms of internal violence," said Jon Alterman, the Middle East program director at the Center for Strategic and International Studies in Washington. "There are a lot of unsettled scores and no ongoing political process that seems likely to address them."
If the Democrats win in November, these type of assessments will undoubtedly clash with their calls for a rapid and comprehensive withdrawal.
By that time, U.S. troop strength is expected to shrink with the pullout of many of the 30,000 "surge" forces that poured into central Iraq last year. The Pentagon predicts to be at 140,000 soldiers by July, though that's still 8,000 more than the total before the surge.
Sen. John McCain, the apparent Republican presidential nominee, has predicted that the insurgency will "go on for years and years and years." But, eventually, the Iraqi forces will have to fight alone. It's the often-touted South Korean scenario: local forces someday on the front lines with a U.S. military presence in a supporting role - possibly for decades.
"A thousand years. A million years. Ten million years," McCain famously said in New Hampshire in January. "It depends on the arrangement we have with the Iraqi government."
It depends, too, on whether the Iraqis and their government can hold on. To a far lesser extent, it also hinges on world sentiment - the U.N. Security Council mandate for the U.S.-led force in Iraq is set to expire at the end of the year, which could increase international pressure for withdrawal.
But more than anything else, it depends on whether Americans are willing.
Mary Shuldt is losing patience. Living at Fort Campbell in the Kentucky lowlands, she wonders how many more times her husband and the 101st Airborne Division will be called to Iraq.
"Our families are being ripped apart," she said. "When is enough enough?"
The family of Chris Blaxton, a longtime military policeman in the Army and then the Reserve, has not been ripped apart. And yet America's fissures are apparent in this family, too, as his children reflect on the war and their own futures.
In October, Blaxton was on his second tour in Iraq and just nine days from coming home to Okemos, Mich., when a bomb tore through his Humvee, paralyzing him from the waist down.
His 16-year-old son, Kevin, had been considering enlisting in the Air Force.
Now, he says, "It's not worth it. It's just a war."
But Kevin's sister Rebecca, a high school sophomore, has a different perspective. She watched the nurses at Washington's Walter Reed Army Medical Center help her father, and she'd consider doing the same, someday, for other soldiers - even if it means going to Iraq.
It's not so much that she believes in the war, she says. It has to do with her father and the beliefs that led him to volunteer to go to Iraq.
"When you get the chance to do something for your country," Rebecca said, "do it and don't say 'no."' --- Associated Press writers contributing to this report: Carley Petesch in New York, Chelsea Carter in San Diego, Ryan Lenz in Evansville, Ind., Betsy Taylor in St. Louis, Bradley Brooks in Baghdad.
