Last week, President Trump had what must have been a tense telephone conversation with Turkish President Erdogan. Erdogan’s forces are attacking Kurdish forces allied with America in the Afrin region of Syria. Erdogan has said his forces would pursue the Kurdish militias into Manbij, where U.S. forces are operating with the Kurds against the remnants of ISIS and Syrian forces.

That conversation led nowhere. Neither is Erdogan stopping the attacks against our Kurdish allies nor is Trump declaring them off-limits and promising to defend them. The fact that Trump isn’t ordering our forces to defend the Kurds is a confession of failure. It’s the result of thinking stalemated by the fact that one of our so-called allies — Turkey — has chosen to be at war with a real ally, the Kurds.

The Kurds are one of the many ancient peoples indigenous to the Middle East. About thirty million of them are spread over parts of northern Iraq, southern Turkey, Syria, Armenia, and Iran. A Kurdish autonomous zone of Iraq is rich with oil. But there is no nation of Kurdistan.

When Woodrow Wilson and the other victorious leaders of the allies that won World War One sat in Paris in 1919, carving up old empires and creating new nations, their announced goal was to create nations around self-governing peoples. One treaty created a Kurdish state and another signed shortly afterward dissolved it.

Since then U.S. relations with the Kurds have been an on again, off again affair. We supported Kurdish attempts to overthrow the Baathist regime of Iraq in the 1970s, withdrew support for most of the 1980s, but brokered a peace agreement between Kurdish factions in 1998.

The Kurds have suffered before and since. Typical was the March 1988 attack on the Kurdish city of Halabja by Saddam Hussein’s forces, using artillery and chemical weapons, that killed at least five thousand. We imposed a no-fly zone over Iraqi Kurdistan in 1991, enforced by U.S. and British aircraft.

When Turkey denied passage for U.S. troops entering Iraq in 2003, the Kurds tried to help. They have been an ally ever since.

Kurdish forces — usually characterized as militias but with far more skill, organization, and effectiveness — have been at the forefront of our fight against ISIS for over ten years.

Turkey has always feared and resented the Kurdish population on its southern border. It fears their drive for independence which, if effective, could carve out a large portion of southeastern Turkey and northern Iraq to create an independent Kurdistan.

Turkey has always characterized Kurdish forces as terrorists. Their accusation, leveled at the Kurdish “Peoples’ Protection Units,” also known as the YPG, and the Kurdistan Workers’ Party (PKK), is not entirely inaccurate. The PKK has called for an independent Kurdistan carved out of Turkey and both PKK and YPG have, over the years, allegedly conducted raids into Turkish territory.

That brings us to today. Kurdish forces have formed the backbone of our fight against ISIS, which has ravaged areas of Syria and Iraq. Turkish forces fighting the Kurds have employed airstrikes and tank forces (using German-manufactured tanks) in northwestern Syria.

So far, President Trump has not drawn a red line that the Turks cannot cross. Erdogan has answered his inaction with his attacks, which he now threatens will extend into the area in which U.S. forces would be endangered by them.

The president and his advisors are stuck in the neutrality corner with one ally fighting another. The problem they apparently won’t face is that Turkey is no longer our ally. The facts are overwhelming.

Twenty years ago, I often wrote that Turkey was our most underrated ally. It was a cornerstone of NATO, hosting a huge U.S. air base near its capital of Ankara. The Turkish military often trained with our forces, shared many of our secrets, and — perhaps most importantly — served as a model of how an Islamic nation could bridge the gap between Islam and the West. Recep Erdogan has reversed all that.

Erdogan rose to power on the hard-core Islamist beliefs he was raised on. First as mayor of Istanbul in 1994, he has made his mark on Turkish society. His main goal, on consolidating power, has been to change the secular nature of Turkey’s government created by Ataturk in the aftermath of World War I into a radical Islamist state.

Erdogan’s injection of Islamism into Turkish culture is thorough and continuous. The Turkish military had two jobs: maintain Ataturk’s secularization of the nation and defend it against foreign enemies. Since becoming Turkish president four years ago, Erdogan has purged his nation’s military of secularists and replaced them with Islamists like himself.

Individual rights are repressed in accordance with Muslim ideology. Schools have been re-created to teach that ideology. Journalists are as rigidly controlled as they are in other despotic systems.

Erdogan has broken with his obligations as a NATO member in ways that are intolerable. For example, last year he signed a treaty with Russia and Iran to protect the terrorist Assad regime in Syria. This placed Turkey on the side of two of our most dangerous enemies.

The attempted coup against Erdogan in 2016 led to the arrest of thousands, including the remaining secular senior military officers who hadn’t already been purged. Last year Erdogan, by referendum, revised the Turkish constitution to grant him the power to rule by decree. His popularity in Turkey demonstrates his success in turning it into an Islamist state.

The 2106 coup attempt also led to Erdogan’s demand that we extradite Fethulla Gulen, a Turkish leader who has lived in the U.S. since 1999. Gulenists may have had a role in the coup attempt, but Erdogan has demanded the extradition without presenting any evidence justifying such an action.

Erdogan has no regard for the United States. Last May, after his power was enhanced in the referendum, Erdogan visited Washington, D.C. When demonstrators appeared outside the Turkish ambassador’s residence, a squad of Erdogan’s security detail emerged to assault the demonstrators, injuring several.

One of the biggest dangers Erdogan poses is his sharing of NATO and U.S. secrets. His realignment of Turkey as an ally of Russia and Iran makes it imperative that Turkey no longer receive U.S. and NATO secrets.

Erdogan has purchased Russian weapons, including the S-400 anti-aircraft and anti-missile system, which are incompatible with NATO weapons but of a piece with his ongoing cooperation with Russia and Iran.

Erdogan evidently believes that as long as the U.S. airbase at Incirlik operates, we cannot take any action against him. As valuable as Incirlik is, we can’t allow it to become a hostage enabling Erdogan to control our policy decisions.

To paraphrase what Lord Palmerston told the British parliament in 1848, America has no permanent allies and no permanent enemies, only permanent interests and it is our duty to pursue them. Turkey was an ally and has now encamped with our enemies. The Kurdish forces fighting against ISIS are — so far — a faithful ally. President Trump should declare our Kurdish allies off limits to Turkish attacks, and enforce that “red line” with military force if necessary.