Syria will be the biggest blot on the Obama presidency, a debacle of staggering proportions. For more than four years now, the war has festered. A country has been destroyed, four million Syrians are refugees, Islamic State has moved into the vacuum and President Bashar al-Assad still drops barrel bombs whose shrapnel and chlorine rip women and children to shreds.

For a long time, those who fled waited in the neighborhood. They wanted to go home. They filled camps in Turkey and Jordan and Lebanon. When it became clear even to them that “home” no longer existed, nothing could stop them in their desperate flight toward the perceived security of Europe. The refugee crisis is the chronicle of a disaster foretold.

The refugees do not care what “Christian” Europe thinks. They are beyond caring about Europe’s hang-ups or illusions. They want their children to live. In their homeland, more than 200,000 people have been killed. Statistics numb, but less so when you know the dead. This evisceration of a state is a consequence of many things, among them Western inaction.

American interventionism can have terrible consequences, as the Iraq war has demonstrated. But American non-interventionism can be equally devastating, as Syria illustrates. Not doing something is no less of a decision than doing it. The pendulum swings endlessly between interventionism and retrenchment because the United States is hard-wired to the notion that it can make the world a better place. Looking inward for long is a non-option for a nation that is also a universal idea. Every major conflict poses the question of how far America should get involved.

President Obama has tried to claw back American overreach after the wars without victory in Afghanistan and Iraq. He has responded to a mood of national weariness with foreign adventure (although Americans have not been very happy with Obama’s pivot to prudence). He has tried better to align American power with what is, in his perception, America’s limited ability to make a difference on its own at a time of growing interdependence. One definition of the Obama doctrine came from the president last year when he declared: “It avoids errors. You hit singles, you hit doubles; every once in a while we may be able to hit a home run.” Or, more succinctly, “Don’t do stupid stuff.”

But that’s not enough, as Syria demonstrates. President Obama has important foreign policy achievements, including breakthrough agreements with Iran and Cuba that took courage and persistence. (How those breakthroughs will play out remains to be seen, but they constitute a victory over sterile confrontation.) Elsewhere, however, he has undersold American power. In Syria and Libya he has washed his hands of conflicts that the United States could not turn its back on. Such negligence comes back to bite America, as its experience in Afghanistan since the 1980s has shown. Nobody loves a vacuum like a jihadi. And nobody likes American wobbliness like Vladimir Putin.

In 2011, Obama said, “The time has come for President Assad to step aside.” At that time, as events have shown, the president had no policy in place to achieve that objective and no will to forge such a policy. His words were of a grave irresponsibility.

In 2013, with France poised to join the United States in military strikes on Syria, Obama walked away at the last minute from upholding his “red line” on the Assad regime’s use of chemical weapons. In so doing, he reinforced Assad, reinforced Putin, declined to change the course of the Syrian war, and diminished America’s word in the world — setbacks of far greater significance than ridding Syria of chemical weapons. This was a mistake.

Yes, China and Russia have consistently obstructed concerted action on Syria in the United Nations Security Council. Yes, the shifting array of forces and interests in Syria has been a challenge to policy. Yes, even limited intervention had its dangers. But, no! Such ruination was not an inevitable outcome.

At multiple stages, if Obama could have mustered the will, the belief in American power, there were options. The Syrian aircraft dropping those barrel bombs could have been taken out. A safe area for refugees might have been created. Arming the rebels early and massively might have changed the course of the war. Counterfactuals, of course, don’t carry much weight. We will never know. We only know the facts of the Syrian nightmare now seeping, in various forms, into the West. Syria, broken, will be the rift that keeps on giving.

In Libya, Obama bombed and abandoned. In Afghanistan, Obama surged and retreated. In Syria, Obama talked and wavered. He has been comfortable with the pinpoint use of force — the killing of Osama bin Laden for example — but uncomfortable with American military power.

Syria is the question the Obama doctrine must answer if it is not to be deemed modest to the point of meaninglessness.