On May 23, 2003, I attended the Baghdad news conference at which the U.S. viceroy, Paul Bremer, announced he was dissolving the Iraqi army.

I thought of that day when I read of Wednesday’s confrontation between 19-year-old student Ivy Dietrich and Jeb Bush, who had been blaming President Obama for the rise of the jihadis. She told the former Florida governor, “Your brother created ISIS.”

Dietrich’s claim was a bit too blunt but still right on the money. It should serve as a warning to 2016 presidential contenders: Using the Iraq war as a political club against the opposition can boomerang. Obama, too, has erred on Iraq, but the origins of ISIS go back to before he took office, and stem from mistakes made at the beginning of the war.

On that May 23, Bremer axed tens of thousands of military officers with guns who were let go without pensions or severance. His order propelled the birth of an armed Sunni resistance among ex-Iraqi officers, which morphed into al-Qaeda in Iraq and ultimately ISIS.

Bremer’s decision reflected the lack of coherent planning in the Bush administration about what to do after the U.S. invasion. Before the war, the U.S. military had recognized the danger of disbanding Iraq’s armed forces, at a time of high unemployment and great social upheaval; it had planned to dissolve the units closest to Saddam Hussein, while vetting the rest and creating a smaller force that could help with rebuilding the country.

But George W. Bush’s emissary, Bremer, changed the plan, apparently without consulting top U.S. military or State Department officials. After Bremer’s announcement, I rushed to knock on doors in a Baghdad neighborhood populated by senior Sunni army brass, and heard the same message over and over: “We laid down our arms, as you asked in leaflets dropped from your planes, and this is how you reward us. We will fight you.”

I was reminded of that warning last month on a trip to Iraq, where U.S. military officers who have already served multiple tours in the country are trying, again, to rebuild the Iraqi army — so it can help drive ISIS out of Iraq.

U.S. officers, despite their dedication, admit there is a feeling of déjà vu. The U.S. military worked hard to rebuild Iraq’s security forces in the 2000s, but they virtually collapsed during the ISIS invasion last summer. The Shiite-led government of the previous prime minister, Nouri al-Maliki, had packed the corps with officials chosen on the basis of Shiite sect or bribes to political officials, including Shiite militiamen who had lived and been trained in Tehran. Professional military men, some of whom were initially returned to the ranks, were mostly kicked out under Maliki.

“The (current) Iraqi army was not formed on any real structure, and lacks a common understanding of leadership,” I was told by Raad al-Hamdani, a former general in Hussein’s army. “This is an army without discipline or good morale. People who came from Iran were given ranks.”

The capture of the key Iraqi city of Ramadi by the Islamic State Sunday, after Iraqi security forces fled, further underscores the accuracy of the general’s words.

Hamdani, a respected military professional cleared of any political crimes, now lives in Amman, Jordan. That’s because former Sunni army officers became targets for assassination by Shiite militias. Many of these officers have valuable expertise that would be helpful in defeating ISIS, but because they are Sunnis (and former Baath party members) few if any will be called on to help.

Under such conditions, many ex-officers grew beards and morphed into jihadis in the last decade and became the backbone of al-Qaeda in Iraq. Others played key roles in ISIS, which helps explain why the organization has been fairly successful militarily. One reason why ISIS was initially welcomed into Mosul, the large city the group made the seat of its so-called caliphate, was that it is home to tens of thousands of retired Sunni officers.

Bremer’s and George W. Bush’s Iraq errors of omission and commission continue to resonate 12 years on.

None of this absolves Obama from responsibility for his role in ISIS’s emergence. Most glaring was the strong U.S. support for Maliki after he lost a close election in 2010. U.S. officials should have tried harder to help the winner, Iyad Allawi, form a government. As a secular Shiite, Allawi was far more skeptical of Iran and he might have allayed the Sunni resentments that helped fuel ISIS. I also believe Obama should have pushed much harder to keep a small U.S. troop presence in Iraq.

But to blame the rise of ISIS only on Obama requires a blatant rewriting of recent history. The seeds of ISIS were planted when Bush’s policies disempowered Sunnis and empowered Shiite religious parties and militias. Bush opened the door to massive Iranian influence in Iraq as the ayatollahs rushed to support fellow Shiites, which scared some Sunnis into supporting the jihadis.

So, yes, Ivy Dietrich, a careless Iraq war sowed the seeds for ISIS, although Obama’s lack of interest helped facilitate ISIS’s expansion. Instead of using the Iraq case as a political football, candidates of both parties would benefit from greater introspection. It’s time for more serious thinking about how to help clean up the mess that America helped create in Iraq.

Trudy Rubin is a columnist for the Philadelphia Inquirer.