One of the most surprising of President Barack Obama’s legacies may be the eclipse of “Never again” as an aspiration of U.S. foreign policy.

I don’t mean that Obama is the first president to stand by as atrocities unfold. He is not. Just as Obama has watched passively as Syria has unraveled, with hundreds of thousands killed and more than 11 million — half the nation — displaced, so President Bill Clinton did nothing to stop genocide in Rwanda, and President George W. Bush failed to stop the depredations in the Darfur region of Sudan. But Clinton expressed remorse for his inaction in Rwanda. Americans in churches and synagogues demanded that Bush take steps to “save Darfur.” Political will was lacking, but there was at least a sense of unease, even shame, that the U.S. would stand aside as so many innocents were slaughtered.

Syria’s four-year-long descent into hell, amply foretold and arguably the most preventable of the three calamities, has prompted little such soul-searching. Why the change?

It’s true that fewer people have died in Syria (220,000) than in Rwanda (upwards of 800,000), and over a longer time. But it is the most horrific humanitarian catastrophe of the past two decades, U.N. officials have said.

Valerie Amos, U.N. under-secretary general, wrote recently in The Washington Post that ordinary Syrians “have been bombed out of their homes, tortured, abused and denied food, water and health care. Families have been torn apart. Communities have been destroyed. ... During every visit I was asked the same thing: Why has the world abandoned us? Why does nobody care?”

The fashionable Washington answer today is that the world is doing nothing because nothing can be done. Muslims will kill Muslims, Sunni will hate Shia, and the civilized world must watch regretfully from the sidelines until the fever burns itself out. This is always the argument for inaction. We heard it about Tutsi and Hutu in Rwanda, and about Serbs and Croats in the Balkans.

And always the argument refutes itself. If these are such ancient and implacable hatreds, why were people not killing each other a few years back, and why are people in the Balkans no longer killing each other today?

When Syrian dictator Bashar al-Assad began waging war against what started as a peaceful movement for democracy, Obama could have authorized training for a moderate, multi-sectarian resistance. When Assad began dropping shrapnel-filled barrel bombs on apartment buildings full of children — the signature weapon of his war, as machetes were to the Rwandan genocide — Obama could have destroyed Assad’s helicopters or given the resistance the weapons to do so. He could have, with allies, offered air cover for a safe zone in northern Syria where people at least could find some refuge from Assad’s attacks.

At each turn, many people, including his advisers, warned that a failure to act would allow extremists to extend their sway. Now the fulfillment of those warnings — the presence of extremists — provides one more pretext for inaction. Meanwhile more than 3 million children have been forced to leave their homes. “Some years from now the world will look back and ask why so many of us did so little,” former British premier Gordon Brown wrote recently. No action available to Obama would have been risk-free or guaranteed to succeed. Almost by definition, these problems are difficult; that’s why Clinton and Bush also failed to act.

What’s different about Obama is his assertive defense of inaction. Shortly after his re-election, in an interview with The New Republic, he asked, “And how do I weigh tens of thousands who’ve been killed in Syria versus the tens of thousands who are currently being killed in the Congo?” Later in 2013, speaking to the United Nations, he defended U.S. reticence in Syria by asserting that defense of democracy and human rights was not a “core interest” of the United States — unlike, for example, ensuring “the free flow of energy.”

Some may welcome this dry-eyed realism; after all, what good did Clinton’s admission of fault do the Tutsis? Better that people know not to await a U.S. rescue that is never going to come.

Yet if preventing genocide and crimes against humanity is no longer even an American ideal, surely we will have given up something of value. Obama himself seems uncomfortable with the implications of his 2013 doctrine; just this month, he told Thomas Friedman of The New York Times that it is a “core interest” after all “that children are not having barrel bombs dropped on them, that massive displacements aren’t taking place.”

Maybe Obama’s successor will take those words to heart — and act on them.

Fred Hiatt is The Washington Post’s editorial page editor.