American commanders on the ground and in the Pentagon regard the Kurdish militias as indispensable partners.

The following column is the opinion and analysis of the writer.

Perfidy is sometimes necessary to procure or preserve national power, and the mightiest nations, more frequently than the meekest, find themselves in positions where being faithless to friends is the most expedient course. In an American history bulging with examples of calculated treachery, the Kurdish people are unique in having been sold out twice, by President Richard Nixon in 1975, and President George H.W. Bush in 1991.

Now, they face betrayal by a third American president. The Trump administration has announced that the U.S. will stand aside as the Turkish military enters northeastern Syria in a potentially major offensive against the Kurdish-led Syrian Democratic Forces. The SDF has been at the frontlines in the fight against the Islamic State: 12,000 of its fighters have been killed, and 20,000 injured. American commanders on the ground and in the Pentagon regard the Kurdish militias as indispensable partners.

For Turkey President Recep Tayyip Erdogan, the militias are a grave national threat; he believes they are aligned with Turkey’s Kurdish separatists. For Syria President Bashar Assad, the SDF is the immovable object that has resisted his war to reclaim all of Syria.

For President Trump, the Kurds have been no more than an inconvenience since he proclaimed victory over IS last December. Keen to keep his campaign promise of bringing home all American soldiers in the Middle East, he has chafed at the obligation of maintaining a small U.S. military presence in Syria, primarily to keep up the fight against remnants of the IS, but also to prevent Turkey from launching an offensive against the Kurds.

The Kurds, for all their proclamations of shock , have long known how this would end. A people twice betrayed were never going to pin all their hopes on their betrayers. For several months, they have been negotiating with the Assad regime, anticipating American abandonment; but they have a weak hand, and cannot hope for much from Damascus.

In any case, Assad may only have limited agency: His regime is heavily indebted to Russia and Iran. Russia President Vladimir Putin is courting Erdogan ardently, and may find it expedient to let the Turks have their way in northeastern Syria.

In short, the old Kurdish saying, “Kurds have no friends but the mountains,” has never rung truer.

If history is any guide, the Kurds will put up a stiff resistance. Years of fighting with IS have turned the SDF into a formidable force, but the Turkish military enjoys substantial advantages. Very likely, the Kurds will take heavy casualties, and a refugee crisis is all but certain.

If the consequences of Trump’s betrayal are inevitable, he might yet be able to ameliorate some of the pain — and save some American honor — if he follows the example of predecessors who abandoned allies in the past. Gerald Ford signed the Indochina Migration and Refugee Assistance Act of 1975 to allow tens of thousands of Vietnamese, Cambodians and Laotians to resettle in the U.S.; George H.W. Bush ordered Operation Provide Comfort in 1991 to succor hundreds of thousands of Kurds fleeing Saddam’s vengeance; and Bill Clinton ordered Operation Northern Watch to keep them protected from the Iraqi dictator.

Since Turkey is a NATO member, a U.S. military intervention in Erdogan’s offensive once it has been unleashed would breach the alliance; nor can it provide the Kurds arms and intelligence to defend themselves. But Trump can and should act quickly to offer them refuge. He should press European and regional allies to prepare for a massive humanitarian effort.

This could mean establishing safe zones for Kurdish refugees, in Syria and probably in Iraq. In turn, this will require marshaling international pressure on the governments in Ankara and Baghdad.

Trump more than likely will do none of these things: He has shown little sympathy for the Kurds. But Congress can help . Lawmakers, many of whom are outraged by his decision to abandon the SDF, should force Trump’s hand with legislation to give the Kurds refuge in the U.S.

These actions are not only morally incumbent on the Trump administration, they are also crucial to reassuring other American allies, now and in future. The next time America betrays its friends — as history tells us it must — they should at least know that Washington will not leave them to their fate.

Bobby Ghosh is a columnist and member of the Bloomberg Opinion editorial board.