Veterans of the Iraq war have been watching in frustration as Republican presidential contenders distance themselves from the decision their party enthusiastically supported to invade that country.

Some veterans say they long ago concluded their sacrifice was in vain, and are annoyed that a party that lobbied so hard for the war is now running from it. Others say they still believe their mission was vital, regardless of what the politicians say. And some find the question being posed to the politicians - Knowing what we know now, would you have invaded? - an insult in itself.

"Do-overs don't happen in real life," said Gregory Diacogiannis, 30, who was an Army sniper in Baghdad trying to spot militants laying roadside bombs and chased high-value targets in the city of Baqubah. "I have trouble with the question itself just because it lends itself to disregarding the sacrifices that have been made."

Diacogiannis left the Army in 2008, but says even now he feels such a strong attachment to Iraq that he's thought about going back to fight as the country has plunged into chaos since U.S. troops left.

The war became a campaign issue when likely presidential contender Jeb Bush was asked about the invasion ordered by his brother, former President George W. Bush. After days of questioning, Jeb Bush said that in light of what's now known - that Saddam Hussein did not have WMD stockpiles - he would not have invaded.

Other possible Republican hopefuls including New Jersey's Gov. Christie, Sen. Marco Rubio, Sen. Ted Cruz, and Ohio Gov. John Kasich all later gave similar responses.

Aaron Hinde, 33, is appalled at what he feels the U.S. invasion did to Iraq. He served there in 2003, mostly in the volatile city of Mosul, and became active in the antiwar movement after leaving the Army in 2004. He said that he's glad Republicans are being held accountable for the invasion, but that the answer's been known for a long time.

"It's a legitimate question to ask and a legitimate answer should be an unequivocal no," he said.

Marla Keown, who drove trucks in Iraq for a year during her time in the Army Reserve, said it's taken too long for politicians to admit the mistake of a war that killed 4,491 U.S. troops and left countless Iraqis dead.

"It's hard to see the good in war in general - let alone a war that everyone just now is realizing we shouldn't have done," said Keown, 34, now a photographer in Denver.

But many vets, regardless of whether WMD were found or not, found legitimate reasons for being in Iraq. John Kriesel lost his legs when a 200-pound bomb went off underneath his humvee outside Fallujah. He's written a book, Still Standing: The Story of SSG John Kriesel, detailing what he went through.

He said he's proud of what he and his unit did in Iraq to make their area safer. He speaks fondly of Iraqi children he encountered and said he'd do it again in a "heartbeat." So many questions, he said, like whether to invade Iraq or not, are easier to answer in hindsight. "I think it's naive to just assume that we can just wave this magic wand and know what we would do in that situation," Kriesel said.

Kevin McCulley, a former army medic, said Iraqis told him about their struggles under Hussein and he feels there were good reasons to get rid of the longtime dictator. He feels the emphasis really shouldn't be on the decision to invade but on whether the U.S. should have stayed past its 2011 departure date to secure the gains made. Many vets blame President Obama - not Bush - for the current state of affairs, saying he was in too much of a hurry to withdraw.

"There's a huge issue for me about why we left Iraq," he said.

On Friday, Democratic presidential contender Hillary Rodham Clinton said despite the militants' gains, U.S. ground forces should not be sent back to Iraq. She has called her support for the invasion a mistake.

"A mistake doesn't sum up the gravity of that decision," said Matt Howard, a Marine twice deployed to Iraq who now works with the group Iraq Veterans Against the War.

Mike Barbero, a retired general who served three tours in Iraq, said he isn't sure of the value of the hypothetical questions being asked of the candidates and would rather they be pressed on the future. "What are your criteria for putting young Americans in harm's way? What lessons learned did you take away from Iraq and Afghanistan? Then you're getting into the mind of a future commander-in-chief," he said.

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Veterans who served in Iraq react to the recent fall of the city of Ramadi to the Islamic State. Currents, C1.EndText