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 gotcha 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 served as an army sniper in Baghdad trying to spot militants laying roadside bombs and chased high-value targets in the city of Baqouba. "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 Gov. Chris 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 northern city of Mosul and became active in the anti-war movement after leaving the army in 2004.

He's glad Republicans are being held accountable for the invasion, but says that 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, of Denver.

The discussion comes at a particularly fraught time for veterans, who have watched Iraq steadily descend into chaos. In recent days, Islamic State militants routed Iraqi government troops to take control of the city of Ramadi, the capital of Anbar province, despite American airstrikes designed to help the Iraqi forces.

Kevin McCulley, a former army medic, said Iraqis told him about their struggles under Saddam 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.

Clinton has previously 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. He said many vets have been frustrated by the "flip-flopping," not just of the Republican candidates, but of Clinton as well.

Mike Barbero, a retired general who served three tours in Iraq, said he isn't sure the value of the hypothetical questions being asked of the candidates and would rather they be pressed on their criteria for sending troops into a potential future battle.

"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.