It all started with a question to Jeb Bush (who has yet to formally declare his candidacy) that surprisingly proved to be a stumbling block for the brother of former president George W. Bush, who started the war in 2003.
"Knowing what we know now, would you have authorized the invasion?" Megyn Kelly of Fox News asked during a May 11 interview.
"I would have and so would have Hillary Clinton, just to remind everybody, and so would almost everybody that was confronted with the intelligence they got," he replied.
"You don't think it was a mistake?" Kelly followed up.
Bush answered that "in retrospect" the intelligence was faulty but didn't say the invasion itself was a mistake. Not focusing enough on security once the invasion happened and Saddam Hussein was gone, that was a mistake, he suggested.
These weren't the answers people were expecting from the former Florida governor, who will be a frontrunner for the 2016 nomination, and the uproar wasn't just from Democrats, but from Bush's own party.
Rubio also struggles to answer
Conservative pundits shuddered at the damage Bush could do to the party as he clearly wrestles with the Iraq question and his brother's legacy.
"If Jeb Bush sticks to his position — that he would still authorize war knowing what we know today — it will represent a step backward for the Republican Party," Byron York, a Washington Examiner columnist wrote.
"You can't still think that going into Iraq, now, as a sane human being, was the right thing to do," Conservative radio host Laura Ingraham said. "If you do, there has to be something wrong with you."
Bush did damage control, but he bungled that too in subsequent interviews when he tried to explain that he misunderstood the question, and that he didn't like hypothetical questions. It took him a few more days and tries to finally say he "would not have gone into Iraq."
Bush wasn't the only one who struggled with the Iraq question, Marco Rubio joined the club on Sunday, also during an interview with Fox News.
Host Chris Wallace pressed Rubio to answer whether it was a mistake to invade Iraq. They sparred over the phrasing of the question, the use of hindsight when trying to answer it, and whether Rubio had flip-flopped on his position.
The missteps by Bush and Rubio allowed other possible candidates to learn from their mistakes, have their answers ready, and to take some digs.
Other possible candidates
"Knowing what we know now, I think it's safe for many of us, myself included, to say we probably wouldn't have taken that tack," Wisconsin Gov. Scott Walker told an interviewer.
New Jersey Gov. Chris Christie on CNN: "If we knew then what we know now, and I were the president of the United States, I wouldn't have gone to war."
Texas Senator Ted Cruz said: "Knowing what we know now, of course we wouldn't go into Iraq."
"I don't know how that was a hard question," former Pennsylvania senator Rick Santorum said about Bush's handling of the question, adding that he's been asked it "a hundred times."
The Iraq "mistake or not" question is straightforward on its surface, but deciding how to answer it does have deeper challenges for Republican candidates.
Public support for the Iraq War diminished as the intelligence on weapons of mass destruction was revealed to be wrong, as the years dragged on and as more than 4,000 Americans died and thousands came home injured.
Candidates want to be on side with public opinion and so not all of them are eager to defend George W. Bush and to say it was a great idea to go to Iraq.
But they may also be reluctant to say it was a mistake for fear of suggesting that all those lives lost were in vain.
They may also be keeping their base supporters in mind and don't want to risk alienating them. Some Republicans believe, weapons of mass destruction aside, that going into Iraq was still the right thing to do because the world needed to be rid of Saddam Hussein and democracy brought to the region.
What now in Iraq?
The candidates are being asked what they would have done in 2003 and what they would do now to deal with the current conflict in Iraq with the rising power of the terrorist group ISIS. Answering the "what now" in Iraq question is also fraught with political risk.
When they place blame for the mess in Iraq on President Barack Obama, questions are inevitably raised about why the U.S. got involved in Iraq in the first place.
They also have to counter the argument that ISIS was allowed to flourish because of the instability in Iraq that followed the U.S. invasion.
"Your brother created ISIS," a young woman told Jeb Bush in front of reporters, cameras rolling.
Presidential hopefuls will have to offer solutions in Iraq that the American people will be willing to support and sending thousands of troops back there for another long, drawn out conflict is not an easy sell.
The Iraq question was also put to the leading Democratic candidate this week, former secretary of state Hillary Clinton. She wrote in her recent memoir that her vote in support of the war was "a mistake" and that's what she repeated on Tuesday.
Own it and move on, appears to be her strategy, but she too will be dogged by the Iraq question and her various iterations of an answer about the war's validity over the years. Democrats though, are making use of a divided Republican field, putting out videos and reminding voters of who Jeb Bush's brother is and the decisions he made.
Whether they like it or not, Iraq is poised to pose an ongoing challenge for candidates in the months ahead.