The fall of Aleppo just weeks before Barack Obama leaves office is a fitting stamp on his Middle East policy of retreat and withdrawal. The pitiable pictures from the devastated city showed the true cost of Obama’s abdication. For which he seems to have few regrets, however. In his end-of-year news conference, Obama defended U.S. inaction with his familiar false choice: it was either stand aside or order a massive Iraq-style ground invasion.

This is a transparent fiction designed to stifle debate. Five years ago, the popular uprising was ascendant. What kept a rough equilibrium was regime control of the skies. At that point, the U.S., at little risk and cost, could have declared Syria a no-fly zone, much as it did Iraqi Kurdistan for a dozen years after the Gulf War of 1991.

The U.S. could easily have destroyed the regime’s planes and helicopters on the ground and so cratered its airfields as to make them unusable. That would have altered the strategic equation for the rest of the war.

And would have deterred the Russians from injecting their own air force — they would have had to challenge ours for air superiority. Facing no U.S. deterrent, Russia stepped in and decisively altered the balance, pounding the rebels in Aleppo to oblivion. The Russians were particularly adept at hitting hospitals and other civilian targets, leaving the rebels with the choice between annihilation and surrender.

They surrendered.

Obama has never appreciated that the role of a superpower in a local conflict is not necessarily to intervene on the ground, but to deter a rival global power from stepping in and altering the course of the war. That’s what we did during the 1973 Yom Kippur War, when Moscow threatened to send troops to support Egypt and President Nixon countered by raising America’s nuclear alert status to Defcon 3. Russia stood down.

Less dramatically but just as effectively, American threats of retaliation are what kept West Germany, South Korea and Taiwan free and independent through half a century of Cold War.

It’s called deterrence. Yet Obama never had the credibility to deter anything or anyone. In the end, the world’s greatest power was reduced to bitter speeches at the U.N. “Are you truly incapable of shame?” thundered U.S. Ambassador Samantha Power at the butchers of Aleppo. As if we don’t know the answer. Indeed the shame is on us for terminal naïveté, sending our secretary of state chasing the Russians to negotiate one humiliating pretend cease-fire after another.

Even now, however, the Syria debate is not encouraging. The tone is anguished and emotional, portrayed exclusively in moral terms. Much less appreciated is the cold strategic cost.

Assad was never a friend. But today he’s not even a free agent. He’s been effectively restored to his throne, but as the puppet of Iran and Russia. Syria is now a platform, a forward base, from which both these revisionist regimes can project power in the region.

Iran will use Syria to advance its drive to dominate the Arab Middle East. Russia will use its naval and air bases to bully the Sunni Arab states, and to shut out American influence.

It’s already happening. The foreign and defense ministers of Russia, Iran and Turkey convened in Moscow this week to begin settling the fate of Syria. Notice who wasn’t there. For the first time in four decades, the United States, the once dominant power in the region, is an irrelevance.

With Aleppo gone and the rebels scattered, we have a long road ahead to rebuild the influence squandered over the last eight years. President-elect Donald Trump is talking about creating safe zones. He should tread carefully. It does no good to try to do now what we should have done five years ago. Conditions are much worse. Russia and Iran rule. Maintaining the safety of safe zones will be expensive and dangerous. It will require extensive ground deployments and it risks military confrontation with Russia.

And why? Guilty conscience is not a good reason. Interventions that are purely humanitarian — from Somalia to Libya — tend to end badly. We may proclaim a “responsibility to protect,” but when no American interests are at stake, the engagement becomes impossible to sustain. At the first losses, we go home.

In Aleppo, the damage is done, the city destroyed, the inhabitants ethnically cleansed. For us, there is no post-facto option. If we are to regain the honor lost in Aleppo, it will have to be on a very different battlefield.

© 2016, The Washington Post Writers Group