Yes, it is true that there was no al-Qaeda in Iraq when George W. Bush took office. But it is equally true that there was essentially no al-Qaeda in Iraq remaining when Barack Obama took office.

Which makes Bush responsible for the terrible costs incurred to defeat the 2003-09 jihadist war engendered by his invasion. We can debate forever whether those costs were worth it, but what is not debatable is Obama’s responsibility for the return of the Islamist insurgency that had been routed by the time he became president.

By 2009, al-Qaeda in Iraq had not just been decimated but humiliated by the American surge and the Anbar Awakening. Here were aggrieved Sunnis, having ferociously fought the Americans who had overthrown 80 years of Sunni hegemony, now reversing allegiance and joining the infidel invader in crushing, indeed extirpating from Iraq, their fellow Sunnis of al-Qaeda.

At the same time, Shiite Prime Minister Nouri al-Maliki turned the Iraqi army against radical Shiite militias from Basra all the way north to Baghdad.

The result? “A sovereign, stable and self-reliant Iraq.” That’s not Bush congratulating himself. That’s Obama in December 2011 describing the Iraq we were leaving behind. He called it “an extraordinary achievement.”

Which Obama proceeded to throw away. David Petraeus had won the war. Obama’s one task was to conclude a status-of-forces agreement (SOFA) to solidify the gains. By Obama’s own admission – in the case he’s now making for a status-of-forces agreement with Afghanistan – such agreements are necessary “because after all the sacrifices we’ve made, we want to preserve the gains” achieved by war.

Which is what made his failure to do so in Iraq so disastrous. His excuse was his inability to get immunity for U.S. soldiers. Nonsense. Bush had worked out a compromise in his 2008 SOFA, as we have done with allies everywhere. The real problem was Obama’s reluctance to maintain any significant presence in Iraq.

He offered to leave about 3,000-5,000 troops, a ridiculous number. U.S. commanders said they needed nearly 20,000. (We have 28,500 in South Korea and 38,000 in Japan to this day.) Such a minuscule contingent would spend all its time just protecting itself. Iraqis know a nonserious offer when they see one. Why bear the domestic political liability of a continued U.S. presence for a mere token?

Moreover, as historian Max Boot has pointed out, Obama insisted on parliamentary ratification, which the Iraqis explained was not just impossible but unnecessary. So Obama ordered a full withdrawal. And with it disappeared U.S. influence in curbing sectarianism, mediating among factions and providing both intelligence and tactical advice to Iraqi forces now operating on their own.

The result was predictable. And predicted. Overnight, Iran and its promotion of Shiite supremacy became the dominant influence in Iraq. The day after the U.S. departure, Maliki ordered the arrest of the Sunni vice president. He cut off funding for the Sons of Iraq, the Sunnis who had fought with us against al-Qaeda. And subsequently so persecuted and alienated Sunnis that they were ready to welcome back al-Qaeda in Iraq – rebranded in its Syrian refuge as the Islamic State of Iraq and Syria – as the lesser of two evils. Hence the stunningly swift ISIS capture of so much of Iraq.

But the jihadist revival is the result of a double Obama abdication: creating a vacuum not just in Iraq but in Syria. Obama dithered and speechified during the early days of the Syrian revolution, before the jihadists had arrived, when the secular revolt was systematically advancing on the Damascus regime.

Hezbollah, Iran and Russia helped the regime survive. Meanwhile, a jihadist enclave (including remnants of the once-routed al-Qaeda in Iraq) developed in large swaths of northern and eastern Syria. They thrived on massive outside support while the secular revolutionaries foundered waiting vainly for American help.

Faced with a de facto jihadi state spanning both countries, a surprised Obama now has little choice but to try to re-create overnight, from scratch and in miniature, the kind of U.S. presence – providing intelligence, tactical advice and perhaps even air support – he abjured three years ago.

His announcement Thursday that he is sending 300 military advisers is the beginning of that re-creation – a pale substitute but the only option Obama has left himself. The leverage he forfeited will be hard to reclaim. But it’s our only chance to keep Iraq out of the hands of the Sunni jihadists of ISIS and the Shiite jihadists of Tehran.

© 2014, The Washington Post Writers Group